N2Teeth,
There's no database of which I'm aware. However, have you tried looking at the SL Shared Information user guide? It might provide some insight into how sales tax is calculated and applied.
Also, I think sales tax is applied to the total price of merchandise--not per line item. You could, perhaps, back-calculate the per line item contribution to the total tax, but this information isn't stored in SL.
Thanks,
DB