I can accept that most ATMs give 20's; that's what they store, most of them don't have the space for smaller bills.
But several of the local corner stores with a cashback option also only give 20's; I put my milk and whatever on the counter, hand over my debit card and say that I'd like, say, $15 cashback or $30 or $35.
Most of the stores charge 50c to a dollar for using the card. I'm OK with that, it's cheaper than a non-my-bank ATM. But why, oh why, do the cashier's say "No, it has to be 20's only."
No it doesn't. You have fives and tens and I am willing to pay for them. Today, I actually did not have enough money in my account (I get paid tomorrow) to GET 20 cashback.
After a "conversation that consisted of several reiterations of "20's only!" and "But, why?" I put the milk back, because I'm nice that way, but I ended up going across town to my bank (good thing I had enough change in my purse for the bus.)
On the other hand, I kind of love self-check lanes at larger grocery stores, because I can do stuff like ask for $14.75 cashback without getting weird looks from the cashier. As someone who takes buses, underground rails and who has to use quarters for laundry, I appreciate smaller-than-twenties!