tax only one state, the rest tax free?

-- HikaShop version -- : 2.5.0
-- Joomla version -- : 3.4.3
-- PHP version -- : 5.4.43
-- Browser(s) name and version -- : firefox 39.0

I only need to tax California. How do I do that?

Hello,
You'll just have to go through your tax configuration page via "Hikashop->System->Taxes" and add a "Zone" restriction.