any suggestions? POS system development

I was more or less asking about the use of all these undocumented methods.

If you have written app's that interface with receipt printers and cash drawers what is best practice on the use of the methods to OPEN/CLAIM/OPENDRAWER/etc...

My "SQL TRANSACTION-like" mind tell me I want to start loading "purchase" items into a table for an order in an "open-status". Then total up the price - get some $$'s from the client - note the change amount. That's when the drawer opens. I would love to have the receipt already starting to print - then after the app detects that cash drawer is closed then flag the order as a "closed-status".

Now how to translate all that into proper method calls to the OPOS object is my challenge.