It depends on the ATM. When I was in LA, the ones down there were mostly charging 10%. The one here in Portland only charges 5%, but after trekking across town and getting to the mall, they don't have the sell option available today for some reason. Luckily there were two women looking to buy Bitcoin for the first time, so I got to give them all of the important do's and don'ts to keep themselves safe, and sell them $500 worth.