On Saturday December 11 I went to the Bowery Ballroom to see Jesse Malin perform. I was on the main level (where the stage is) standing next to the bar in the back of the room. There was a female blonde bartender with a "fashionable pageboy haircut" serving drinks. I ordered a $5 Budweiser and gave her a twenty dollar bill. She gave me 5 singles back. I called her over and said " I gave you a twenty"....she nodded and then I said " and this is the change you gave me" ( as I showed her my 5 singles). She opened the register and said " You gave me a ten." I said " Okay, I'm sorry" and left her a dollar tip. I am 99% sure that I gave her a 20 dollar bill. I don't think that the fact that she opened the register and looked in really meant anything.( She was doing multiple transactions while mine was taking place.) I did not want to start trouble and ask for the manager because it was her word against mine. ( I assumed that the Bowery Ballroom would have taken the bartender's side over the customer's .) Should I mark my money in the future? Should I bring a flask into the Bowery Ballroom and not purchase alcohol? Should I loudly announce the denomination of money I am handing the bartender in the future? Was it an honest mistake or was I ripped off? My gut feeling tells me I was ripped off.