Most restaurants include a non-obligatory service charge on the bill, which under standard practice is 10% (so much so that "10%" is used in Brazilian Portuguese as a synonym for "tip"). There is no legal obligation to pay, however it is really expected by the staff, and declining to pay it can cause distress and confusion, since it is considered part of the salary. Currently, due to tax law changes, restaurants some times charge 12%, while expensive restaurants can charge up to 15% (or more). You can always pay how much you want. However, paying less than 10% would be seen as a complaint.