In one case for me (Bank of America, 2008, I think) it was 4 transactions totaling under $40, and $140 in fees. This was just when a lot of people were starting to default on their variable rate mortgages, and banks were holding on to every dime they could to offset that. I was encouraged to deposit the money to cover the overdraft before the bank opened, then request a refund. That's what I did, and they refused to refund any of it.. left me in quite a bind.
I canceled the account - I'll never go back to them - and soon as the laws were passed that consumers may opt out of the overdraft "privilege"** I opted out, though of course, they always try to talk me into reconsidering.
** You inform the bank in writing (it can even be handwritten) that you don't want your overdraft privilege, and then they can't charge the fees, instead the deny the charge. They WILL try to talk you out of it.