tax calculation error when discounting

[Cushions4Cancer]

Zen-Cart v1.5.7d
New Install
installed mod Quantity Discount (https://www.zen-cart.com/downloads.php?do=file&id=135)


I seem to be having an issue with the tax calculation when checking out with a discount applied.

If I purchase a single item which doesn't qualify for the discount, the total and tax are correct




If I purchase 2 of the items, which qualifies for the discount:




Order sub total plus shipping
$70 + $9.95 = $79.95

Above total minus discount
$79.95 - $3.50 = 76.45 (so total is correct)

However GST should be 10% of the total ($76.45 / 11 = $6.95) but it is calculating the GST on just the subtotal plus shipping and ignoring the discount figure.

Any ideas of where I might be going wrong ?


Quantity discount settings