Well, most people know what it takes to fill their tanks, so it isn't an excessive amount, it's like $5 extra and you go back for the change. Realistically 90% of people use cards and the ones that use cash put an amount that fits in the tank. I'm not going to put $20 in the tank if $15 puts it right at full, I'll put $10 in and not worry about it.

I remember having pre-paid with cash before.

The machine would take the note and stop the pump when it reached the price. If you overpaid, that's your problem. If you didn't get a full tank, that's not a real problem, you still got what you paid for.

It's sort of like when stations had attendants and you'd pull up and ask them to fill up for a tenner or something.