Unless you are committing fraud, like falsely trying to claim it has a value other than what it actually does, defacing currency isn't illegal. So trying to pas

Unless you are committing fraud, like falsely trying to claim it has a value other than what it actually does, defacing currency isn't illegal. So trying to pass off a penny as being worth 5 cents today by filing it down would violate that law, but if they really were worth 5 cents, it would be fine.