I think I get it, except for this part
This would be done from queries, so I could have a tabbed section to pick the category
Possibly a combo should be used to choose a category and not "tabbed section" (whatever that is) but queries cannot dictate what image a button shows. Nor would I use command buttons to indicate an item that can be chosen unless there was an accompanying visible control to indicate the current count. Otherwise, how would you know if the click added to the count or not? How would you remove 1 from a count without an accompanying minus button, which also would require an image, making this messier?
Anyway, there are tons of results if you Google MS Access POS. That should be the starting point, and if nothing is found that is suitable, it ought to at least shed some light on what is possible and aid in further discussion. No sense in recreating the wheel if you don't have to.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.