Tax Column in MySQL Database

I am working to put together an adaptive payment chain for PayPal, which deposits a percentage of each transaction plus sales tax into my paypal account (primary receiver), then forwards a balance payment to my local contractors (econdary receivers) who administer my local stores and pay our local suppliers. I need to design the adaptive payment code to query my store's MySQL database to quantify the sales tax pertaining to each order, but can't find the table this information is stored in.

Would it be possible to develop a feature (ideally a vqmod) I could apply to each store directory that stores the sales tax amount for each order in a new field ('sales_tax') of the order_total table for each order_id?