Weird...I had almost the exact same thing happen to me today. There's a chain of convenience stores that sells fountain drinks for $.79 ($.85 with tax). I took $.85 cents in with me, and bought a drink. The young lady asked me for $.95. I said, I thought they were.85. She said that they had gone up. When I offered to go out to the truck to get the other dime, she told me not to worry about it. I do frequent that store a good bit, though.