[2.3] Ensure coupon taxes are reset when calculating totals.

Fixes #7780

includes/class-wc-cart.php

@@ -88,6 +88,7 @@ class WC_Cart {
 		'taxes'                       => array(),
 		'shipping_taxes'              => array(),
 		'discount_cart'               => 0,
+		'discount_cart_tax'           => 0,
 		'shipping_total'              => 0,
 		'shipping_tax_total'          => 0,
 		'coupon_discount_amounts'     => array(),

readme.txt

@@ -138,6 +138,8 @@ Yes you can! Join in on our [GitHub repository](http://github.com/woothemes/wooc
 
 == Changelog ==
 
+* Fix - Ensure coupon taxes are reset when calculating totals.
+
 = 2.3.7 - 18/03/2015 =
 * Fix - Allow saving of empty download expiry date on orders.
 * Fix - get_total_discount() function with certain tax setups.