I am not a QW Page employee but I do install and teach NewViews.
What you describe is not how the sales journal works but the way the purchase journal works. I have just confirmed it on a set of books.
If you try to enter an Item total amount on the sales journal you will get an error.
You can enter an after tax amount in the item total on the purchase journal and it will calculate the tax and before tax amount.
At least that is how it is working on my copy of 2.19.
Could you check again that you are on the sales journal and not on the purchase journal.