Later? Maybe, maybe not, depending on the magnitude of the error.

I did have an experience similar to Jmichaels, though. I paid at a Dunkin Donuts in Bloomfield, NJ with a ten dollar bill and got change for a twenty. It was the morning rush hour and I only noticed it as I was outside walking to my car. I went back inside and said, nicely, that there was a problem with my change and.... Before I could even finish the sentence, the manager comes over and starts yelling "it's too late for that! You left the store. No adjustments!" and pointed to a sign that says "Count your change before you leave" (or something to that effect).

I just sighed and said "Well, that's too bad. You see, you gave me ten dollars too much but, since it's too late to give it back, I thank you for buying my lunch."

You should have seen the look on his face as I walked out and all the customers waiting on line got a good laugh.