currently, the only place you can go to buy and sell bitcoins is Coinbase which is under IRS investigation, if you ever bought or sold bitcoin there, IRS will audit your tax. Bitcoin users are completely screwed in the USA.
I assume you mean that Coinbase is the only place for you to buy your coins, right?
Nowadays there are so many other services where you can buy and sell Bitcoin. Best thing is that they offer a wide variety of options to make a deposit.
That being said, what happened with Coinbase regarding the IRS, is just a start. I wouldn't be surprised that at some point other exchanges will undergo the same treatment from the IRS.
Bitcoin is a growing industry where the government is (according to them) missing out on tens of millions in unpaid taxes. It's more than worthwhile for them to open the hunt on people through their exchanges.