thing is, all tills are different. i work in Morrisons on the kiosk, & have covered shifts in the petrol station a couple of times (did one tonight actually!) & the 2 systems are totally different & thats within the same store!
basically the only reason they want experience is cos they want people who're used to dealing with customers, which is definitely something that takes a while to build up. in my first week working, i was practically in tears on 2 separate occasions due to customers being downright rude to me (ok, i made a mistake - but hey, i was new, & i had a sign on my checkout stating that!). now i've developed a bit of a "screw you" type attitude, there's no way i'd let a customer get me to that stage these days!