The problem with airtime kiosks

Every time I go buy airtime at my local Spar, I have to go through a wad of cash being spit out by the machine before it eventually accepts a note or two. I find this highly annoying and feel extremely conscious of people around me as I have to continually feed R100 notes into the machine, only to watch them being rejected until it finally swallows one. I don't blame cashiers for not wanting to swop you out for silvers and take all their change, and carry large quantities of change around just for this purpose is just weighty. There have been days where the machine hasn't taken any of my money so, irritated beyond belief, I went without. This kind of non-service is just lousy for business as I'd tend to abandon whatever else I'm buying at the time and go get them at wherever I do find airtime easily available. And I don't think I'm the only one. Why can't they just install service machines at tills that do printouts - like so many other places offer?