maybe also look at the concept of currency, values & make your own demonination with the children, or for the setting?
Cut discs of card & cover with gold, silver & bronze foil, if the tills ordinarily used in shop role play are too small for the new units use calulators and baskets?
On a side note, this is a good site for the leanrning involved with money
https://www.ncetm.org.uk/resources/25170
Hth best wishes