This is a user to user only forum. We can't answer tax questions for purchases made in one country for a user who lives in another country. I doubt the tax will be waived for you at purchase. It wouldn't be waived if you travelled to the US and bought a phone. Apple will typically collect the tax required in each location around the world where the product is sold. Whether you can get a refund of that tax, you'll have to contact Apple directly, but I highly doubt it.
Also, be advised that iPhone Warranty is NOT international. If you have an issue with the phone once back in your country, you'll need to go back to the country of purchase for warranty support. It is ALWAYS best to buy your phone in the country you live and will use it.