I'm sure that sometime in the dim and distant past I've been into a garage that actually had a little dish of 1ps, so if you did go over by that, they just took one out of the bowl for you, and also if you had one p left over from buying something that was ending in 0.99 (such as a sandwich) you put the change in the dish. Unfortunately I can't remember for the life of me where this garage was! but I imagine that it's a country garage, rather than one in surburbia.