Seems to be a braintree limitation.
Taxes. Unless otherwise stated, all fees are quoted exclusive of any applicable value added tax (VAT). For the sake of clarity, the Braintree Services are in scope of the exemption from VAT of Art. 135 (1)(d) of the EU VAT Directive 2006/112/EC.
It is your responsibility to determine what, if any, taxes apply to the payments you make or receive, and it is your responsibility to collect, report and remit the correct tax to the appropriate tax authority. PayPal is not responsible for determining whether taxes apply to your transaction, or for collecting, reporting or remitting any taxes arising from any transaction.
https://www.braintreepayments.com/legal/policy-updates
It looks like braintree can integrate with taxamo for vat calculation. I use Spark w/Stripe myself, so haven't needed to attempt integration, so I can't say how easy/difficult it would be to integrate with Spark.
https://www.taxamo.com/support/getting_started/braintree_integration/