1.  In the General Ledger, create a new Tax account that will be designated as a "holding" account for the tax withheld.
2.  In Accounts Payable, Records, create an invoice for the vendor that is subject to the NC 4% withholding.
3.  Create a new Credit memo, using the Tax account and Accounts Payable Summary account for the distribution.
4.  The Credit memo should be 4% of the total invoice amount. 
5.  Apply the Credit memo to the invoice to reduce the balance of the invoice by 4%.
6.  To report on the total withholdings for the quarter, run a General Ledger report filtered on the tax account

For more information on the new 4% North Carolina tax, Refer to NC Department of Revenue.