I'm having trouble with Better Together and Group Discount. The Group Discount is incorrect when Better Together discount is applicable to the cart. Group Discount is correct if Better Together is not applicable. The Group Discount is too low by an amount that equals the tax on the Group Discount on the Better Together discount.

Example:
Product 1 price is $100; Product 2 price is $50. Better Together discount is 50% off Product 2 price if Product 1 is also purchased. The Group Discount is 15%. I want the Group Discount to apply to the subtotal minus the Better Together discount. So the cart subtotal is $150 ($100 + $50). The Better Together discount is $25 (50% of $50). The Group Discount should be applied to $125 ($150 - $25) and equal $18.75. But Group Discount calculates $18.53. The $0.22 difference equals the tax (6% in my case) of the Group Discount on the Better Together discount ($25 * 15% * 6% = $0.225).

I also have Quantity Discount installed (v1.12.1) but this problem does not occur with Quantity Discount and Group Discount.

Zen Cart v155e, Better Together v2.5.3, php 5.6.31. The Better Together and Group Discount (as well as Quantity Discount) setting for Include Tax is false, and the setting for Recalculate Tax is standard.