How can I force tax per line item to then calculate in the tax summary on Purchase and Sales Orders?

How can I force tax per line item to then calculate in the tax summary on Purchase and Sales Orders?

Dear Sir/Madam

I have set up my products that we provide so that the cost is calculated on the line item inclusive of tax rate automatically. My issue now is that the Tax Rate calculation then doesn't get replicated in the Summary area under sub totals with out then adding an additional 20% tax rate to the grand total. How can this be rectified without then having the put an adjustment figure in so that it calculates correctly.

Yours Sincerely
Andrew Devall BSc.(Hons.)