Use this tab to connect tax codes to income types. You can connect only tax 
codes of tax type Tax Withhold. When an income type is entered for a 
customer invoice line, the tax withholding code connected to income type will be 
automatically suggested. These tax codes will be automatically suggested only if 
no valid tax-exempt exists and the selected delivery address of the customer is 
subject to tax withholding. In order to enter default tax withholding codes, at 
least one customer income type must have been defined.
If the Mandatory option is selected in the field Tax Withholding Code 
in the Income Types window, it is always required to specify a tax 
code for that income type. By entering the '%' symbol in the field Income 
Type, you can specify that all income types are connected to the tax 
withholding code.