It is not 'box', it is 'bucks', an informal term for USD, Indian Rupee and a few more currencies.
I had read somewhere that originally 'buck' referred to deer i.e. money given to buy/exchange deer skin in ancient times.
ell.stackexchange.com/users/3187/Maulik V
Adding to Maulik V's answer, there's a slight difference between the pronunciations of box /ˈbäks/ and bucks /ˈbəks/
I know it's not easy to differentiate for some (and up to some point),
but if you'd try to listen carefully, you'd be able to distinguish properly (also, context clues).
(pronunciations were taken from http://www.merriam-webster.com/ )
ell.stackexchange.com/users/21978/shin
When referring to money or equivalents, the box can refer to the cash register (AmE) or till (BrE) or possibly wherever money is stored safe deposit box
It should not be confused with a vault which has a different context.
An equivalent meaning to box is bank which is when a waiter or waitress carries money on their person without going back to a central register
Each wait-staff carries their own bank which is then reconciled at the end of the night.
A technical use of the word box is where one keeps their stock (AmE) or share (BrE)
holdings
When you short against the box you use your holdings (as collateral) to sell against it (self) Also, when security houses used to manually transfer investment certificates, those operations were in an area generically called the box , where security was very high.
ell.stackexchange.com/users/26439/Peter
One use of box to mean money, in the UK at least, is the term Christmas Box.
This is a gift of money (a tip if you like)
traditionally given to tradespeople on the first working day after Christmas.
Hence the term Boxing Day which is now a public holiday.
https://en.wikipedia.org/wiki/Boxing_Day gives more information.
ell.stackexchange.com/users/31818/amay
In the danish language, you can use the sentence "Han tjener boksen" to describe that someone earns a lot of money.
Directly translated, it means "He earns the box".
In danish "boksen" can mean both "the box" (like a cardboard box) and a money deposit vault (the very large kind that banks always seem to have in the basement in robbery movies).
Not sure if this helps though.
But in danish it does make sense to use the word box as a slang for money.
ell.stackexchange.com/users/31858/Gertsen
This is not the first time that I see people refer to money as "box" ( see here 0:12 )  I searched in my dictionary and I didn't find a meaning like that, so I think about two options:   a) Maybe there's another word which sounds similar but is written differently. b) It's the word and it's not in all the dictionaries
Does the word "box" also have a meaning of money?
ell.stackexchange.com
<word-meaning>
ell.stackexchange.com/questions/85137
ell.stackexchange.com/users/12430/Judicious Allure
One use of box to mean money, in the UK at least, is the term Christmas Box. However, this may not refer to "box", but  "bucks" - an informal term for USD, Indian Rupee and other currencies.   This may actually refer to 'bucks'. 'Box' might refer to a Christmas box in UK contexts.
This may actually refer to 'bucks'. 'Box' might refer to a Christmas box in UK contexts.