At the moment, Paythen doesn't support showing or adding tax separately as line items on the payment page. Any payment amounts in Paythen plans should include any applicable taxes.
We expect to support Stripe Tax as well as an alternative simple tax input in the future for countries with single tax rates - eg: GST in Australia, Singapore, New Zealand etc where only a single tax rate applies.
If you're interested in this, let us know via the chat icon so we can better prioritize it.