Iran stops taking US currency for oil

Iran hasn't been selling oil in US currency for a few months now.  Not many know this, and if they do know, they don't think much of it.  Iran is the second largest OPEC crude oil producer.  Wonder why gas in the US is so expensive?  That is one of the reasons.  

Iran stopped talking US currency saying "it's a worthless piece of paper".  The weak dollar is also blamed for the crippled purchasing power of Iran.