Say I go to a brewpub. Order a draught beer and a burger. Happy hour so the price is $8 instead of $11. Don't feel like tipping $3 - it seems exorbitant. But service was polite and efficient, $2 on what could have been an $11 is enough but doesn't communicate that I was pleased. So I tip $2.50. Does the server think I was just too cheap to give her the extra fifty cents, that I'm a "cheap tipper" even though it's over 20%? Do servers go strictly by %, do they expect customers to round up to the nearest dollar?