As an American, I always put my card into the pump itself and then fill up. No guessing, no change, no even going inside for a normal visit. One time I went i

As an American, I always put my card into the pump itself and then fill up. No guessing, no change, no even going inside for a normal visit. One time I went inside to buy a can to fill up, and I also paid upfront for a gallon, which made the pump cut off automatically. I've never tried to pay for an unknown amount of gas with cash, and never felt any need to.