Taxes and contracts can a big impact on the people they affect, though. A typo on a bank note has no direct effect on any users. It's an aesthetic problem, not a functional one.
I've been a cashier, and trust me, we had more important things to do than examine bills with a magnifying glass looking for spelling errors. If a bill seemed suspicious at a quick glance, I swiped it with the counterfeit detector pen, and if it came out fine, I shrugged and put it in the register.