What I'm describing is not exclusive to the USA. It's just how fuel purchases are made when paying at the pump isn't an option, so you have to go in & do the transaction with a human behind a Point-of-Sale machine. The person at the cash register doesn't know how many gallons or liters you need. So you have to tell them. But they want to know the corresponding cash amount, not the volume of liquid. So you have to do the math yourself in order to tell them the dollar amount to charge to your card. 🤷🏼‍♀️ I don't know how to make this any clearer.