I'm from Brazil and I'm goingo to USA in january, so i need to buy dollars.
Here in Brazil every currency exchange done have to pay a tax that is usually 7%.
But we don't have to pay that tax in cryptocurrency. 
So i was wondering if i can do it through bitcoint or other cryptocurrency.

* First i would buy bitcoin in Brazilian currency to my wallet through any exchange (Real to bitcoin)
* Second i shall sell this bitcoin in any exchange that accept USA Dollars. (Bitcoin to Dollar)

But i dont have anywhere to keep this money. 

Have anyone already done this in any currency? 
Can indicate how have you done?