You can Rebuild the Cube using VB and DSO (the PI for Analysis Services. A better Method may be to use a a Tax dimension that is hidden in your cube and referenced by the Cube. You can then process the cube and tax dimension and have the Calc reference the Dimension member. Or for ease of use have the tax dimension as a visible dimension with a range of tax values possibly boken into some hierarchy Say Fed, State, Local, Sales etc etc. And allow the user to interact with the dimension making the calculation useable by all tax members.
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