Thanks for the reply, i was considering this at first, but it's exactly what I want to avoid. I want it to be even simpler than using actual cash - because it's possible. This needs some Apple approach developers:)
The proposed solution is actually at least as simple as cash, I would think.
The customer who wants to pay you in LTC/BTC knows how to use it, even if your cashiers don't.
A posted QR code for those who have smartphones, and a printed account number (or maybe an easy to type URL where they can quickly copy it on their laptop/tablet/whatever they have with them) for those who don't but still want to make physical transaction in crypto.
All you need is a little monitor on your WinXP/Cash register that shows incoming transactions to the account.
This might be nearly zero development if block chain explorer offers an account balance API.
At that point the customer can say "I just sent X.XX coins to your litecoin account." The employee looks at the monitor window, when it says "incoming transaction" for that exact amount, it's the customer's payment. If you want to wait a specific number of confirmations that's ok too.
Since it's going to be the customer's responsibility to send, this solutions is truly "easier than cash" for the employee, who just waits for the payment to show on the screen.
And it's a very simple transaction for a bitcoin or litecoin user to make, using their own wallet or equipment.