All multi-taskers to the check-outs

It's all going smoothly enough. Beep... Beep.. Beep.
And then you want to buy an onion.
And the entire system breaks down.
And they have to call a supervisor, who comes over and scrutinises the onion and talks into a head-set and rushes off with it to get advice from above. And I am thinking, "Look, could you not have just taken a wild guess? I would be prepared to give you 15p for it, if that sounds reasonable."
Ten minutes later the "supervisor" comes back with the onion and says, " 13p."
Beep!