Create Subtotals

I would like to be able to add subtotals for extended_cost and tax_amt for the following query and then a net_cost that is a sum of extended_Cost and tax_amt for each of the orders I have. I believe I need to somehow use the Group by command, but with so many fields from so many fields, I am not sure where to start.
Here is my code so far...


Code:

SELECT Customer.First_Name,
Customer.Middle_Name,
Customer.Last_Name,
Customer.Address,
Customer.City,
Customer.Region,
Customer.Postal_Code,
Customer.Country,
Customer.Customer_ID,
Store.Store_Address,
Store.Store_City,
Store.Store_State,
Store.Store_Zip_code,
Store.Store_Phone_Number,
Store.Store_Fax_Number,
Orders.Order_ID,
Employees.LastName,
Employees.FirstName,
Item.Item_ID,
Item.Taxable_Nontaxable,
Order_Line.Price,
Order_Line.Units_Purchased,
Order_Line.Discount,
Tax_Table.Tax_Rate,
'Extended_Price' = (Order_Line.Price*Order_Line.Units_Purchased*(1-Order_Line.Discount)),
CASE WHEN
Item.Taxable_Nontaxable = 1
THEN
((Order_Line.Price*Order_Line.Units_Purchased*(1-Order_Line.Discount))*Tax_Table.Tax_Rate)
ELSE
((Order_Line.Price*Order_Line.Units_Purchased*(1-Order_Line.Discount))*0)
END AS Tax_Amt
FROM Orders
INNER JOIN Order_Line ON Orders.Order_ID = Order_Line.Order_ID
INNER JOIN Customer ON Orders.Customer_ID = Customer.Customer_ID
INNER JOIN Store ON Orders.Store_Code = Store.Store_Code
INNER JOIN Employees ON Orders.Sales_Person_ID = Employees.EmployeeID
INNER JOIN Item ON Order_Line.Item_ID = Item.Item_ID
INNER JOIN Tax_Table ON Orders.Store_Code = Tax_Table.Store_Code
WHERE Orders.Order_Filled = 0
ORDER BY Orders.Order_ID
COMPUTE SUM((Order_Line.Price*Order_Line.Units_Purchased*(1-Order_Line.Discount))) BY Orders.Order_ID