ooof, I had that happen once. Used to be these shitty gas stations where I went to college called Busters Bi-Lo. They only took cash, and would round to the closest $1, and they pumped your gas for you. Super aggressive assholes, too. But they were always 10-15 cents cheaper than anywhere else.
They ended up going out of business because they kept selling shitty gas, and eventually fucked up a whole bunch of peoples cars and couldn't afford to pay out.