Types of Cash Discount Clearing 
Use
This function uses the document type to control how the cash discount should be cleared.
The standard system contains two document types:
The cash discount amount is not taken into consideration when the invoice is entered.
The cash discount amount is only posted to a revenue account when the invoice is paid.
The cash discount amount is credited directly to the account to which the costs are posted when you enter the invoice. For example, if you are posting an amount to a cost center, only the invoice amount minus the cash discount amount is posted to the cost center.
Prerequisites
The following settings are made in Customizing for Invoice Verification:
(Invoice Verification ® Incoming Invoice ® Maintain Document Types and Number Ranges ® Document type)
Activities
The Post Invoice Document: Initial Screen appears.
The system then determines the terms of payment from the first purchase order allocated.
If a fixed cash discount is specified in the invoice, you can enter this amount in the field Cash disc. In this case, the system ignores the terms of payments suggested by the system or entered by you.
You can branch from the item list to the header screen and check or change the terms of payment by choosing Goto
You can also change the default document type in the document header.