In case you update your tax settings in shopify follow the steps below to update it to your Merchant Center.
Tax settings are updated only once using AdNabu, during the onboarding process.
In case the settings have been changed, you can go to Merchant Center and delete the previous settings.
Then you need to come back to Google Shopping Feed App and click on the "copy tax settings" button.
This will ensure the updated taxes is copied to your Merchant Center.