Quantity based Sales Tax

Hello all,

I want Sales Tax calculated on Qty not on value for example:

Qty in Tons     S.Tax per ton       Amount Rs.
3.480                  6306                    21,945.00
0.30                    6306                       1,892.00

the above Sales Tax 6306 is fix per ton.

Although i setup it and that calculate correctly but without clicking "Additional Tax information", so when i define or mention then they should calculat and second issue is when i go to create another PO with different UOM like "each" they show error and not work other then UOM "Ton"

if any body have some relevant doc pl. send me, i wil really appreciate.

waiting for immediate response.

Thanks