The most common method that those of us who are blind use to distinguish bills is to fold them differently. Different people use different techniques; there is no right or wrong way of doing it. I leave my $1’s unfolded, fold $5’s in half the short way, and fold $10’s the long way. My wallet has two sections for cash, so I put $20’s in a separate section and leave them unfolded.
Folding currency often allows us to handle cash reasonably well, but it has serious limitations. Before we can fold a bill, we need to find out its denomination by asking a sighted person or using a machine. This often means that we cannot independently verify that we are being handed the correct change for a purchase, for example. This may be somewhat less of an issue in a crowded store where others in line might notice if we are being shortchanged, but in other situations, such as in taxicabs, there may be no way to check because there may be no witnesses around when it comes time to pay.
Our currency-folding systems are also very vulnerable to tampering by other people. I once had three bills in my bureau drawer that I thought were $100’s, but I went to use two of them at different times and was told that they were $1’s. I suspect that someone who was living with me took the $100’s out of my bureau and replaced them with $1’s, since she had done other things that made me inclined to suspect that, but I cannot be sure, since it is possible that the cashier was lying to me or that someone I asked to identify the bills might have kept them and given me back $1’s in their place. One may point out that I should have immediately gone to the bank with the money rather than keeping it in my house, and in retrospect I would agree with that. Nevertheless, this story does present issues that sighted people would not have–and that I would not have either, if I could distinguish a $1 from a $100.