For retailers (mostly) outside the US, the account-based Tax settings are not applicable.
To apply other taxes such as VAT or GST to your feed so that they match your store:
Click the Edit on any non-US Google feed in your account:
On the next page use the OTHER TAXES Tax Rate field to enter the appropriate percentage of tax to be added to your prices:
Click Save Feed once complete
When back on the Feeds page, click Send Feed to have your changes processed by Google. Note that Google processes feeds typically within 2 hours