Options required are:
none: for current behaviour
exclusive: as discussed here Automatically collect tax on subscriptions
My use case is to have AU-GST inclusive as a line item on on receipts.
Access to Stripe tax is an opt-in that can be requested here https://stripe.com/en-au/tax
Currently it appears that when a Stripe subscription using Ghost is created then it can be modified/updated via the dashboard to include tax for subsequent receipts.
I would be prepared to make or assist with a pull request for change, but first would required some help/guidance with how stripe product is created and best approach to modifying admin UI to add the options.