When it comes to paying on a self service till I'm asked to choose my payment method. As a user (and designer...) I find this extra step a little annoying. Why should I be forced to differentiate between this information?
The till should be able to pick up on what the payment method is, or at least a number of standard ones: cash; card (including contactless); voucher/coupon.
Depending on how soon/what stage the business wants to limit payments to, the till could accept payment at any point or, alternatively, only accept payments after a trigger - such as clicking 'Pay'.