Retail software (real shop, not on the web)

My son-in-law runs a small shop selling antique furniture and general bric-a-brac for which it is important that he maintains a strict log of incomings and outgoings for the shop. At the moment, he manually records every transaction in a old-style ledger but would like to move to a rather more modern way of doing things (i.e using computers). At the moment he has a WordPress website which my daughter and I put together using ‘Market Theme’. This has been proved to be extremely effective but I’m not sure that it could easily be adapted to his requirements. So, what we’re looking for is software which allows my son-in-law or one of his assistants to log into the system and select one of a number of options each of which is a simple menu driven process .. for example, to enter a new customer’s details, check in an item for sale, check out an item when purchased, arrange deliveries etc. Also the system should be able to generate daily reports of incomings and outgoings, scheduled deliveries etc. Clearly all this data is contained within some form of back-end database. The software will only be accessed in the shop (which you can assume will have broad-band access) but it would be useful to generate reports etc from web-based clients.
An ex-colleague has some experience with Microsoft’s Visual Basic for Access (VBA) which allows this sport of stuff to be done but I’m sure that there is a more modern approach to solving the same problem.
So I would be interested in forum members’ views on whether WordPress is a suitable platform for building such an application and, if so, are there any nice themes or plug-ins or whatever available to get us started ? Otherwise does anyone know of any off-the-shelf software to do this sort of thing.
Please don’t let me have to resort to the dreaded Visual Basic on Access stuff !!!

Thanks
Ron