Verify your tax rates are loaded in Magento
Magento 1 is no longer supported. New Magento 1 account connections will no longer be supported, please use the Magento 2 integration. Learn more about this here.
Here's how to verify that TaxJar rates are loaded in Magento.
Once you connect the plugin with the TaxJar API Token, you will have the rates loaded for your nexus states.
You can look under menu Sales -> Tax -> Manage Tax Rules in Magento to see that the state rates were loaded: