Comment by gampleman

In my country the norm is for tips to be rounding based rather than percentage. So if your bill is 327.5, you would pay 350, effectively a "keep the change" sort of gesture.

I have certainly starred them in the eye and waited for them to ostentatiously count out every last penny when the service was truly abominable. It's a fairly effective way to give feedback.

You can also of course round up higher, so in the previous example for exceeding expectations you could round up to 400.