You can:
1) Leave some money, in the form of bills or coins, when you take your
receipt up to cash register to pay the actual bill
2) Leave a quantity of coins or bills that covers the amount of the bill
plus a tip
3) Use a credit card and specify a tip amount.
What exactly is the mystery here?
I can remember when people used to tip waitresses with coins, back
when the purchasing power of the dollar was higher.
--
"Remember when teachers, public employees, Planned Parenthood, NPR and PBS
crashed the stock market, wiped out half of our 401Ks, took trillions in
TARP money, spilled oil in the Gulf of Mexico, gave themselves billions in
bonuses, and paid no taxes? Yeah, me neither."