My 5% vat on purchase invoice are not always give me correct figure. Please what is the solution
You need to demonstrate your situation, but note that tax exclusive differs from tax inclusive.
Tax exclusive 100 + 5% (or + 1/20th) = 100 + 5 = 105
Tax inclusive 105 - 5% (or -1/21st) = 105 - 5 = 100 (not 5% of 105 or 5.25)