* Tweak - Clear the shipping discounts before calculating them again.
* Tweak - Calculate the cart total using the partial cart totals.
* Fix - Fixed wrong discounts in the shipping costs when working with the extension 'WooCommerce AvaTax'.
* Tweak - Tested compatibility with WP 5.3.
* Tweak - Tested compatibility with WC 3.8.
* Fix - Fixed issue when applying a discount to a non-taxable shipping method.