While one can add products, taxes and discount coupons to an order in any sequence, it seems that the only supported workflow (as of WooCommerce 4.7.0) is:

1- Add the line item(s) (the products)
2- Re-calculate tax for the order
3- Add a coupon

If one tries this combination in a different sequence, the final discounts and tax amounts will be wrong (see support ticket 3483484 for more information).

I reckon the system could be improved by implementing one of the two options below:

A) Start supporting products, taxes and coupons being added in any sequence when creating orders via the admin interface (that is one less thing for the users to worry about) or

B) Properly enforce the supported workflow. For example, the "Add Tax” and “Add Coupon” buttons could be disabled until the user adds at least one product to the order; and the “Add Coupon” button could actually remain disabled until the tax is calculated. It is a simple way to guide the users through the right workflow.

Thank you for considering this.