Tax rate for product from database

Hello,

I am creating hikashop sync. tool with accounting program and one of synced items are orders. When I create order I have to set right tax amount so customer would receive appropriate tax rates.
Is there any way to fetch tax namekey used for customer in orders directly from database? Problem getting it from database is that there could be different taxation rules for same tax category so I would have to decide which to use according to customer zone and other thing's. I am wondering if there is simplier way achieve this?

Thank's in advance.

Robertas.