by 'cash register', You mean a POS (point of sale, cash drawer, printer, maybe display)?
you need a FM solution with the standard functionality for other sales - and some methods to 'empty the drawer' at the end of a day, methods to enter payments (cards, cash,) easily, etc.
todays POS printers (ie Star, Epson tm t20, 88) will have USB and connectors for a cash drawer, controlled by the printer driver (FM). So, there isn't much special. Create a layout for the printer, add tables and functionality for 'the end of a day', easy entering amount payed, selecting items (maybe touch display, barcodes), etc.
we don't have displays anymore for our POS - customers will have the computer display (special layouts) for that
so, You need to google for POS, check out the functonality of the all-one systems - and build Your own. You'll find a lot of infos for drawer, barcode-readers, printers, etc.
Keep in mind that there are a lot of quite cheap units out there... But there are still reasons to build a FM based POS!
aare there any books or references that teach that -hopefully in non techie language...?
"are there any books or references that teach that -hopefully in non techie language...?"
That is a completely unrealistic requirement.
since a POS is nothing but a 'standard' accounting/ordering solution (not sure about the wording) with an addition (POS), You could check for this kind of SW.
a pure accounting solution will focus book keeping, what could be a little different...
you might try a google search like 'how to set up a POS system' - there are some whitpapers available, that's just one piece in the puzzle..