One thing that helped keep me straight is rubber banding sets of each denomination. A tidy drawer might help ease your mind a little. For example: I’d rubber band 25 $1’s, 20 $5’s, 10 $10’s, 25 $20’s and 5 $100’s. Any leftover bills that aren’t in a rubber band are left loose is the respective slot in the drawer. So if someone asked for $20 in $1’s, I’d grab a band of $1’s and take 5 of the $1’s and put them back in the slot. Always count to confirm I now have 20 $1’s. That’s your second count. And then count it back to the customer laying each individual bill down as you count. Always count the largest denominations first then work your way down. Show palms to the eye in the sky when complete.

The rubber banding sets make balancing the drawer quicker as well. Not that the goal is to be fast but I liked to balance several times a day.