Not in restaurants. Not in taxis. Of course, a waiter will be very happy if you do tip, and the taxi driver will be very surprised.
This is something a lot of tourists find a little confusing and sometimes unfair, but it’s part of the local culture. When you pay at a restaurant there is a sales tax and a service tax already included.
In Peru, everything comes with the tax built-in as part of the final price, so what you see on the restaurant menu, the supermarket or the department store is what you are going to be charged. Salons, spas and barbershops expect tips but not at the 15% rate. A couple dollars will suffice.
Credit cards? They are widely accepted. But if you ask for a discount (at a crafts market, for instance) you will be asked to pay in cash.