Before you post a credit note or a debit note, you should verify the document totals, and specify whether the credit note or debit note includes the invoice discount (if one applied). You can also enter a comment for the debit note or credit note.
To verify discounts and document totals:
If a discount was applied on the original invoice to the items and miscellaneous charges that you are now crediting or debiting, check the discount that appears on the Totals tab, and edit the discount percentage or amount, if necessary. More...
If item prices include tax, the amount of the included tax is displayed on the right side of the screen. It does not affect the calculation of the credit note amount.
If you need to change tax information for the customer, you use the Taxes tab. See Changing Tax Amounts for Order Entry Documents for more information.