I am working from spain but depending on where an invoice is issued (Mainland or canary islands) the type of Tax is different. I want to automatically assing the vat percentage on invoices following this rules: 

• If the invoice is issued in Canarias (Geographic Site = Gran Canaria) to an entity in Canarias (Postal Code starting with 35XXXX OR 38XXXX): The tax is 7% IGIC
• If the invoice is issued in the Mainland (Geographic Site = All Offices EXCEPT Gran Canaria) to an entity in Canarias, Ceuta, or Melilla ((Postal Code starting with 35XXXX OR 38XXXX OR 51XXXX OR 52XXXX): The tax is 0% IVA
• If the invoice is issued in the Península ((Geographic Site = All Offices EXCEPT Gran Canaria) to an entity in the Mainland and Balearic Islands (Any Postal Code between 1XXXX AND 50XXXX EXCLUDING 35XXX AND 38XXX): The tax is 21% IVA
• If the invoice is issued in Canarias (Geographic Site = Gran Canaria) to an entity in the Mainland, Ceuta o Melilla (Any Postal Code between 1XXXX AND 52XXXX EXCLUDING 35XXX AND 38XXX): The tax is 0% IGIC

I can´t create another company for canary islands, as I already have different companies for different countries and canary islands is part of the spain branch.