While trying to find the solution to the incorrect order total in Edit Orders, I found that function eo_update_database_order_totals in admin/includes/functions/extra_functions/edit_orders_functions.php calls function eoGetOrderTotalTax in admin/includes/classes/editOrders.php. For Quantity Discounts, MODULE_ORDER_TOTAL_QUANTITY_DISCOUNT_TAX_CLASS does not exist, so the routine returns zero. This value is subsequently subtracted from $order->info['tax'] and a little later from $order->info['total']. As a test to see if the lack of this ...TAX_CLASS was the source of my problem, I fudged the return from the routine with the tax on the quantity discount. Now when I reran my test case, the order total was correct, but the now the tax was too high by the tax on the discount. I am so confused now I must be missing the obvious. Any help would be gratefully appreciated. I really need to make this work for our store.