You've just seen a reason why to avoid tourist trap restaurants in the centre of Prague.
Just today there is an article published in Czech newspapers about these service charges in the centre of Prague.
They write that English speaking inspectors got these additional charges 5-15 % in many restaurants they checked.
That never happened when they spoke Czech.
In one of the restaurants the staff didn't return enough change back.
Source (in Czech): http://www.novinky.cz/ekonomika/343108-jsi-cizinec-mas-priplatek-uctuje-ho-vetsina-kontrolovanych-restauraci-v-praze.html
My own experience is somewhat different from Jan's, I would say for a dinner or evening beer drinking we usually tip around 10 % and even more (but also less) if it is convenient when rounding.
Of course we go to our favourite places so the service is good
(it wouldn't be a favourite place otherwise :) ).
When the bill is high the percentage tends to get lower, even considerably.
For a lunch in a fast-food restaurant I do not tip at all, of course.
travel.stackexchange.com/users/18611/Vladimir F
I am not aware of any "common" rule around here except that tip is almost always given by rounding the price up to next multiple of 5 or 10 CZK.
Which makes the usual amount depend on the price quite a lot, considering that normal pub where commoners go to lunch the lunch costs around 100 CZK.
Tip is not mandatory.
It is quite common, but usually not that high.
It would only reach 10% if you were really satisfied.
Often it ranges around 2-8 CZK for 100 CZK depending on the rounding.
travel.stackexchange.com/users/18609/Jan Hudec
Tipping isn't mandatory by definition.
Gratuities may be added under certain circumstances as menus often explain in advance (e.g., for a table with unusually many guests), but that is part of the bill, which is mandatory – at least, this is how it works in the USA.
My experience with the Czech Republic is limited, but when I tipped a waiter in Brno a few years ago, he seemed pleasantly surprised.
A local hostel employee had accompanied me at the time, and explained that tipping is somewhat unusual there.
I see from @pnuts' link that tipping may be more expected than my hostel friend thought though – maybe especially in Prague where tourism is more common and people are more accustomed to receiving or even relying on business from foreign customers.
It's still tipping though; it's not mandatory .
I'd still tip at the rate I'm used to in the USA if I were lucky enough to return today, but only for satisfactory service.
travel.stackexchange.com/users/9801/Nick Stauner
The most commonly used rule for tipping here is: Between 5 and 10 percent.
I think that it's necessary to provide some background to the prices as well
: Most restaurants have large profits on drinks, not only on meals, therefore you quite often pay even for plain water, because they don't want to lose their profits.
However, no tips are included in the prices (this may differ if you pay by card).
Sometimes, there's an extra payment for service, but this is mostly in places you don't want to visit for a generally bad price/quality ratio.
Can you give no tips at all?
Yes, of course, especially if you weren't satisfied.
Can you give larger tips than 10 %?
Yes of course, especially if they were willing to fulfill your special wishes, were really friendly etc.
It doesn't hurt to give some feedback, especially if something was extremly good or bad.
As always.
travel.stackexchange.com/users/3262/yo'
Everywhere I've been which isn't the centre of Prague, the most common tipping practice is to round up 10 to 19 crowns.
If you've spent LOTS of money (say 2000kr)
then you might consider a little more.
Tipping is a demonstration of satisfaction and politeness, not of wealth.
I have had arguments with waiters because I tipped too much
and they thought I was showing off my wealth.
Not surprisingly this situation is becoming less and less common!
In the centre of Prague, tip as you would anywhere else (in a European capital city).
The Czechs have learned fast. :(
travel.stackexchange.com/users/26999/user19666
Here's what I do as a long-term resident: If the restaurant is self-service (e.g. McDonalds)
I usually drop a few 1-2 crown coins into the tip jar, if I have any.
If the restaurant is on the cheap side (less than 10 euros for a full meal), I usually round up to the closest unit of 10, and then add another 10 crowns.
E.g. I would pay 200 for a bill of 183 CZK.
If it's a fancy restaurant, I usually pay a 10% tip and round up to the closest unit of 10.
All of the above is optional and no one would give you the stink eye for paying your exact bill, but people are grateful if you do leave a tip.
travel.stackexchange.com/users/9009/JonathanReez
Is it mandatory to tip in Czech Republic? I went to a restaurant and in the end I was shown a ticket with the bill and an handwritten paper with extra 10%.  I read somewhere that tipping is usual but the service was so bad that I was decided not to tip.   What is the general practice?
What is the rule regarding tips in Czech Republic?
travel.stackexchange.com
<tipping><czech-republic>
travel.stackexchange.com/questions/34139
travel.stackexchange.com/users/3736/nsn
While tipping is not mandatory, it it common to tip between 5 and 10 percent, or to round up 10 to 19 crowns. Tipping is less common in fast food restaurants. In the centre of Prague, tip as you would anywhere else (in a European capital city). Tipping is not mandatory in Prague. However, if you do leave a tip around 5% to 10% of the bill is considered acceptable. In central Prague. Do as you would in any European capital city. It is unusual to tip in fast food restaurants.
Tipping in Prague is usually around 5 to 10% of the bill. In central Prague the amount of the tip is the same as any European city. No tipping in fast food restaurants. Tipping is not mandatory.