Too much change

I had a great teaching moment for my kids today. And it was also a little commical, but sad in the same way. I took my kids to the gas station for a milkshake this afternoon, but I was too lazy to go in with them so I sent the boys in with a $20 bill. They soon came out with 2 shakes and a slurpee for Ally, and $16.00 in change. I knew this was way too much, so I got my lazy rear out of the car and went in to fix the problem. The first cashier looked at me like "okay what do you want me to do about it?", and he told me he didn't have any clue how to help me. And so he asked another cashier to help, who also looked at me like I was crazy, and asked me "what are you wanting to do?" and she quickly had 2 other cashiers looking over her shoulder. I felt like I had 2 heads or something. All I wanted to do was pay for what we bought. After about 10 minutes, they decided to return the first transaction, and to just ring me up for the stuff again. They couldn't believe that I came into to correct this problem. That is what made it sad to me. They didn't even know how to fix this mistake. They had no clue because they said no one has ever come in before complaining of too much change. I hope my kids learned. They probably don't even know what was going on, they just stood there happily eating their milkshakes!!