It is optional in most places in the US. They normally ask if you want the receipt. Lots of people say no. I only say yes when I need to report expenses.
It is not really optional, it is always printed I think, and just thrown out by the cashier if you say you don't want it. If you do self checkout in my experience it's always printed. I think maybe gas stations are the only place where it asks you if you want a receipt.
It depends on the place. I know a couple of small, independent cafe/takeouts that don't print it and don't even ask you if you want one. They'll give you one if you ask. (One doesn't even give you a paper bill, it's displayed on a tablet at the cashier.)
Come to think of it, 7-Eleven is the same way, you have to ask for one.