Looks like you're kind of in the middle of a redo of the data, and need to run a number of update queries to set the initial values on Tax Rate, Tax Status, and so on, for the test data on the Orders table.
UPDATE QUERY FOR TEST DATA
Assuming that there was already data in the [Tax Status] and [Tax Rate] fields on the [Orders] table, here's an example update query to set the [Taxes] amount, based upon the [Price Total] in the [Order Price Totals] table.
Code:
UPDATE [Orders]
SET [Orders].[Taxes] = [Order Price Totals].[Price Total] * [Orders].[Tax Rate]
WHERE [Orders].[OrderID] = [Order Price Totals].[OrderID]
AND [Tax Status] = 1
ORDER DETAIL CHANGES
You need to determine when you are going to calculate the Taxes on the order - IMHO It seems like it belongs on the Order Details Screen, and should be recalculating after any Order Detail change at the same time as the Total Price column is recalculating. On the other hand, there is a good argument that Taxes should have its own tab just like Shipping.
INVOICE CHANGES
Your invoice should have a line near shipping to pick up the value from that [Taxes] field, just like you are picking up the [Shipping Fee] field, and your [Invoice Total] field at the bottom of the Invoice should be updated to add that in as well.