You are seeing inconsistent results on the transaction after applying a single use exemption certificate. You may see the transaction as exempt in the AvaTax document details, as well as the AvaTax Admin Console, but the NetSuite summary shows tax. Other exemption mechanisms such as Entity/Use Codes do not seem to change the tax shown on the transaction summary.
Log into the AvaTax Admin Console
Navigate to Settings > Exemption Certificate Options
Select "Optional" for both United States and Canada