Q - If manual changes to commissions or sales tax amounts are made during order entry on page 3 of COP, why do those amounts have to manually be entered again during Order Billing? 

A - Let me explain a little bit of history behind the billing screen so you know why the system is designed the way it is.  A long time ago, when Macola was in charge of maintaining these codes, a user who entered an order could only access the order header screen (1st page) and the order line item screen (2nd page).  The user could not access the billing screen (3rd page) until the time of billing selection.

After we took over and started to maintain the code, many users mentioned that they would like to be able to access the billing screen during the initial order entry time. This would help them to enter, say, freight or misc. charges, which they can determine ahead of time. Also, customers like to enter the prepaid amount for the order.  Then the freight, misc. charges and prepaid amount can be printed on the order acknowledgment so the customers know what to expect. So for these kinds of reasons, we introduced a global setup flag in Global Setup -> COP_Func -> Order Billing Screen:
    2. Show Billing Scrn During O/E for 'O'-Type ? 

Now you have the flexibility to enter billing screen information during the initial order entry. This is mostly a positive thing. On the other hand, the sales tax and commission amount is usually calculated based on the amount of the orders. It is calculated initially based on the original order amount. But you can't know for certain that the amount will stay the same. For one thing, you could do a partial back order.  The customer can call back and change the order. Since billing selection is the final step to determine the order total amount before the invoice is printed, the system has to recalculate the sales tax and commission amount again based on the final order amount. 

If you need to manually override the sales tax or commission amount, we suggest that you not bother to manually change them during the initial order entry time. Only do that at the billing selection time. The screen below shows fields enclosed in ed rectangles, which will always be recalculated at time of billing selection.