Karma and practicality converge nicely in the case of a small check. If the check is $5 and I give the server a $10, it has such a greater effect than the same tip amount on a larger bill -- mostly for being unexpected. You'll get a smile, and -- if you should ever return to the establishment, you'll be remebered. As a rule I would say that I hugely overtip on small bills and tip "very well" (>20%) the rest of the time. Most people tip badly. As a result, most servers are pessimistic, but I would have to give the server $100 bill at 8PM to get the kind of reaction I can get with a $10 at noon --
2hp