When I pay a restaurant bill with a credit card, I’ll either round up the tip over 20% (e.g., if the bill is $38.40, I’ll give an $8 tip), or I’ll make the tip 20% plus whatever amount it takes to round up the total bill ($37.16, then I’ll tip $7.84 to make the total $45). If I paid cash in either of the above circumstances, then I’d leave an $8 tip. When I pay any other bill, I pay the exact amount.