We keep them on an Excel spread sheet containing the date, time, quantity/caliber, PAL # and stock number of the product. A separate spread sheet is likewise kept for the sale of pellets (yes for air guns). Both are done to comply with Ontario's Ammunition laws.
Originally there was a requirement to record the name and address of the buyer as well. While the law was never changed and technically it still "should" be recorded to "comply with the law as written", a good while ago the CFO issued a circular saying that due to privacy concerns they would no longer be "checking for name/address". However, like I said, the law was never amended, so if the Attorney General got a burr in their butt they could pull the Business Firearms Licences (BFL's) of any Ontario retailer "not" recording the name and address along with the other required information.
There is nothing in the law that I have seen that says "how long" we have to keep the records, so we have quite a number of years worth.
They DO NOT get sent anywhere, achieved at some secret location, transferred to some main frame etc, they are on a single stand-alone machine (where I work - that's the way "we do it", others may differ - there is not list of specifications as to how or where it must be stored).
And YES, every 6 to 8 weeks the Regional CFO stops by and amongst his other checks (guns properly locked up in show cases, warehoused guns stored in a secure lock-up, not exceeding our total amount of ammunition etc) he "does" check the sales logs. It's almost always simply a "look to see that we are doing it" - he has never made a note, made a copy - in fact one of the few times he commented was when he saw that we had recorded a temporary licence number issued to a US hunter (the number is way longer than a PAL/RPAL so it really stood out).
And yes, if you have a BFL and sell pellets, similar records are kept (just don't need a PAL to buy them - any "Government issued photo ID is fine". If you don't have a BFL then NO RECORDS are required when you sell pellets (figure the reason for that one???)
This was probably another one of those "see Toronto, we are taking steps to protect you" laws that serves no other purpose than "perception of taking action".
More recently, possibly due a number of issues with "failing to check when selling ammo or stolen/forged PAL" it has been "suggested" that we confirm the identity on the PAL with a second piece of photo ID. Since this isn't the "law" we have not implemented it - it's onerous enough already just complying with the law as written.