While I like the idea...this is IMO, more than a module and more of a complete application. Things like FIFO require tracking the cost per unit on each inbound shipment, the separation of the goods cost from the shipping cost among other considerations.
Schedule "C" items would include many many things that are not part of the cart at all like, hosting fees, advertising(pay-per-click etc etc), telephone, computing equip, depreciation, and the list is long.
The cart currently does not have the tables to record any of these ancillary costs, and then double entry requires a whole other realm of tracking.
The cost of say Quick Books, or maybe another Open Source application for this can take the Zen Cart info and include it in the bigger picture and it might be wiser to find/select a viable Open Source canidate and develop a module to export the Zen Cart info to.
JMO and 2 cents



