Gas

I made a decision, and it goes as follows:
One day when I get a car, I'm going to go to the gas station, and fill that sucker up.
And I'm going to fill it up with $19.99 worth.
So as I'm giving the guy my $20 bill, he'll look at me strangely, and possibly ask
'Why?'
And I'll just shrug, put my penny in one of those charity cups right in front of his face,
and leave.