**Total** – Calculates the total for an order.
**SubTotal** – Calculates the subtotal of all order forms for an order.
**HandlingTotal** – Calculates an order's handling total.
**ShippingSubTotal** – Calculates an order's shipping subtotal.
**OrderDiscountTotal** – Calculates the order group discount amount. It is the total of order-level discounts of all line items in all shipments in all order forms of an order group.
**OrderGroupTotals** – Calculates order group totals.
**TaxTotal** – Calculates the tax total for the order.
## Change the default calculation
By inheriting from the default implementation of the interface, DefaultOrderGroupCalculator, you override the calculations. Just override one or more methods in DefaultOrderGroupCalculator.
## Change the default validation
The default implementation validates that the total is not negative after the calculation. To change the behavior, override the validation methods, depending on which validation you should override.