Pass it by.
I frequently buy my gas here but no more. I stopped in yesterday. Filled my gas tank, bought 4 items inside. After paying with cash, I asked the attendant if I could have change for a $20. Very rudely,he said no, he needed his change. Period. I walked to my car then turned around and went back inside and returned the 4 items I had purchased. If I could have returned my gasoline, I would have. If the guy would have been polite about the change I would have understood. Oh, it was 3:00 in the afternoon when the school kids stop and buy their junk food. I am quite sure he had plenty of change for a $20.