I had to take a cab to work this morning. The 20 minute ride ended up costing $25.75. I paid with debit, and the machine asked me if I wanted to add a tip. I declined. Am I a horrible person? (Eta- I never take cabs for this distance, so I really don't know. If I take a short ride, I always tip to bump it to $15.)

Protocol for tipping waiters is pretty established (I'm not saying it's always followed, of course), but it's not so clear in other areas. I usually tip my hairdresser, but there have been a couple of times when one person washed my hair and another cut it, and I didn't know how to divide it, or even if it was possible (since I pay for almost everything with debit or credit cards).

What about fast food workers? I generally tip delivery people for food, but not for packages or bigger deliveries. Barristas? Coffee shop workers?

I also worry sometimes that by tipping electronicly, the money doesn't get to the right people, but I never buy things with cash, and bank machines only give out $20s. Is this just paranoia?

Who else do you tip? How much? What are your criteria?