Tipping in the US is getting out of hand. It's always been customary for situations like table service (wait staff are paid less than minimum wage and rely on tips to make up the difference). More and more point of sale systems have the tip prompt built in and it usually lets you opt out or pay a custom amount.
Some bars and restaurants will include an automatic 20% "service charge" so they can pay the workers a better wage. In Minnesota where I live, the law requires the establishment to inform customers in advance, but that's not necessarily the case elsewhere. Look over your bill before paying. If the mandatory charge is there, a tip is not necessary.
If I have to stand in line to buy something, no tip. The person just handed me a cup of coffee or a sandwich. They just did their job for which they receive a wage. For bartender service, usually a dollar tip per drink is customary.
As for pint fills, there's generally no measurement law like in Europe. Here it's considered a "nominal" value. Different for gasoline--every state has weights and measures enforcement and gas pumps must be calibrated and certified. Same for scales at grocery stores--a pound of meat or produce had better be a pound.
It would be nice if we had a system like in some other countries, where tipping isn't a big thing and service workers were paid a decent wage. But tipping is ingrained in the culture in the US and Canada.