Realize when you return home you will have to declare the device to customs in your country unless your duty-free limit is high enough. You do not say where you live. In the USA many states also have "use tax" which is basically local sales tax recovery made on any purchase made outside that state.
I suspect you are unlikely to get a very specific reply to your question. I have researched this for many similar questions and see no indication of Apple doing tax-free sales online, or tax refunds, or even tax-free in physical stores themselves. The exception is in conjunction with perhaps one or two stores per country and Global Blue.
Apple Store locations with GlobalBlue service
https://www.globalblue.com/brands/apple
I also advise against buying a phone in another country. Buying an iPhone in one country to use in another country can have many problems:
LTE Find the right iPhone for the right country or region. - http://www.apple.com/iphone/LTE/
E.g., Using American iPhone 5 in Europe - https://discussions.apple.com/thread/4593901 - Yes, but no LTE support.
Warranty restriction! - http://www.apple.com/legal/warranty/products/ios-warranty-document-us.html - "IMPORTANT RESTRICTION FOR iPHONE, iPAD AND APPLE TV SERVICE. Apple may restrict warranty service for iPhone, iPad and Apple TV to the country where Apple or its Authorized Distributors originally sold the device." <-- The warranty does not outright deny warranty coverage in other countries but there are many limitations to the effect they almost certainly will refuse to do repairs under warranty or even repairs at all except in the country of purchase. The device would have to be sent to a friend in the country of purchase to handle any repair claims because Apple will not handle international shipping.
