Computation of Tax on Cancellation

Hi,

I want to know Suppose i purchased one product of $100 today corresponding to which there was tax of $10 today and today we have Vertex_release_401 on our system after 2-3 months we cancel the same product and at that time there is some change in the CTQ-vertex update suppose it is now Vertex_release_403 so on cancellation ?

1) Will the tax be computed based on the purchase time tax rate ?

2) or will it be computed based on the current vertex update release ?

3) If it would be computed based on the current vertex release then can we delete the CTQ data of previous updates of vertex and if yes then which all tables do we need to truncate for the same ?