Reusing an account for the replacement hire is the tempting shortcut and it is the one that hurts later. Six months on, when you are trying to work out who processed a suspicious refund, every transaction points at a name that two different people have used.
Disable the leaver, create a fresh account for the new hire, and set the permissions deliberately rather than copying the previous person if their role is not identical. Also change any shared passwords the leaver knew — the till is not the only door.
This is also the moment to look at what that person could do: if a leaver had price-override or void rights they did not need, that is a good prompt to tighten the template for the role rather than just for the individual.