I recommend AGAINST this personally...Assuming you use any real or even half hearted accounting program which takes into account your company/business (Quickbooks, etc...), and other various costs to run it, that would be a much much better solution to begin with.
Developing this at all would be a waste of developer resources when there are literally tons of paid/free solutions around already. Those solutions can also take care of things way out of the scope of a single cart/web solution such as hiring people, other costs to acquire products to sell, Paypal fees, etc...