Bizarre Tax calculation

[hfxracing]

ie. tax on $999 (tax inc.) + $10 (tax inc.) freight - $10 inc. discount - should equal $90.82

I think what he is trying to to tell you is that the shopping cart & to be correct by law should calculate as follows:
Price
Shipping
TAX (you must show customer you have tax in there)
Total
Discount

If you put the discount anywhere before you charge tax you would be applying it to the discount. When it should only be applied after tax.
I think that is what RodG is trying to tell you. I could be wrong.