Do they? I certainly don't - it's just a wad of notes. I'd probably notice if the one on top didn't have a "20" on it, and that's about it. When I spend it I'm also just looking to see if it has a "20" on it.
I hate speding dollars. All the bill sizes being g the same, and the colors similar. Too easy to make mistakes. I feel for the blind...how do they cope?
I really don't know. Even as a seeing person you need to have your wits about you, and I think most people sort notes by value in their wallet. Most other countries have notes whose size and color differs by value, so it's much harder to make mistakes.
In the US, IIRC they have a trusted person sort the bills by denomination for them -- like a friend or a bank teller -- and then they fold them into different orientations so they know what they've handed to a checkout clerk. No way for them to prevent being shortchanged, unfortunately.
I guess technology could help though - this would be a great application for smart glasses.
Some countries chose different physical sizes and/or embosed bumps in the corners.