$5s and $1s are fine, but a lot of people quote a standard $2 for breakfast, $3 for lunch, and $5 for supper and a $2 bill reduces both breakfast and lunch by one bill. Since I have to go to the bank anyways to get change (I usually don't have enough $5s or $1s for tips, and the only place that reliably will break a $20 without a purchase is a physical bank) there's no difference in requesting a $2 bill versus a $1 bill. If someone's grabbing $40 out of the ATM and exchanging it during purchases, it might be possible to get the exact change that you want, but it's not always available (nor really the job of a store to give specific denominations other than the minimum required to make the change needed.) A bank or credit union is much more reliable to get change made at, and at that point requesting a $2 bill versus a $1 bill isn't really asking a whole lot more.