Mixed VAT rates on same purchase invoice including out of scope

Feature Request
1

Feature requested
I would like to have the option to have purchase invoice line items with all VAT rates including out of scope and VAT exempt items.

Typical use case
Some of the invoices I have, for example mobile charges, may include a mix of VAT categories. For example roaming charges are out of scope, while monthly charges are subjected to 20% VAT.

How I would expect it to work
When creating a purchase invoice the VAT drop down should show the current VAT rates and two additional rates:

  1. Out of scope
  2. Exempt