[Vouchers] Excl. tax is calculated incorrectly when moving back in checkout process

[drummer83]

Description

Follow up of #11117.
There are different tax calculations depending on the way the checkout process is finished. This requires a product with taxes excluded from price and a payment method with transaction fee.

EDIT: This also seems to happen for tax incl. in price.

• Finishing all three checkout steps in a row while adding a voucher in step 2:
  • CORRECT: Tax on voucher is calculated including the transaction fee.
    
• Leaving step 2 without adding the voucher and then going back from step 3 to step 2 to add the voucher yields this:
  • NOT CORRECT: Tax on voucher is calculated excluding the transaction fee.
    

Expected Behavior

Both ways should provide identical results.
Both ways should provide the result shown as 'correct' above.

Actual Behaviour

Both ways provide different results.
The second way provides the result shown as 'not correct' above..

Steps to Reproduce

1. As enterprise user set up a shop with a voucher, a product with tax excluded from price and a payment method with transaction fee.

Way one:

1. As customer put that product in your cart (make sure your order total is higher than the voucher amount) and proceed to checkout.
2. Finish step 1 of the checkout.
3. In step 2 add the voucher code and select the payment method with transaction fees.
4. Proceed to step 3 and check the order summary.

Way two:

1. As customer put that product in your cart (make sure your order total is higher than the voucher amount) and proceed to checkout.
2. Finish step 1 of the checkout.
3. In step 2 DO NOT add the voucher code but select the payment method with transaction fees.
4. Proceed to step 3.
5. Bo back to step 2.
6. Add the voucher code and select the payment method with transaction fees.
7. Proceed to step 3 and check the order summary.

Animated Gif/Screenshot

See images above.

Workaround

Severity

Your Environment

• Version used:
• Browser name and version:
• Operating System and version (desktop or mobile):

Possible Fix

[drummer83]

Hi @rioug,
I just realized that this also happens for tax incl. in price actually.
I added an 'EDIT' comment in the issue above.