Check the zip code's Tax (%) on the Delivery Rates list – any value other than -1 overrides the state rate (the list shows -1 (state%) next to the state's own rate when it's inheriting). If your state uses the address-based TTR tax system, the rate may instead come from the address's resolved jurisdiction (shown under the zip as a TTR: line). Finally, whether tax is charged on the delivery fee itself depends on the Charge taxes on delivery? setting.