Show tax amounts in the grid instead of an X in the Tax column on AR billing invoice

Currently, when we bill a customer that we need to charge sales tax, an X appears in the Tax column instead of the actual amount of tax for that line item. The TOTAL tax for the invoice is calculated at the bottom; however, customers want to see the tax for each individual line item. I currently end up whiting out the X and handwriting in the sales tax, which does not look very professional.