Alright, you answered my question.
But if you do trade bitcoins for something else (not money), that wouldn't be taxed under income gain? You would pay sales tax when required by companies because they pay their taxes, but if you just trade them with a person for something. Like on eBay, when you purchase something you don't pay sales tax.
Are we talking about what the law requires here, or are we talking about what people tend to get away with most of the time?
The IRS doesn't let you get away with avoiding income tax by bartering. As an example lets say I do some work for you (perhaps painting your house?). When it comes time to pay me for the work I've done, instead of paying me with cash we barter and you agree to give me your dining room set (perhaps you are planning on replacing it?). As far as the IRS is concerned, I earned an income equivalent to the fair market value of that dining room set, and you earned an income equivalent to the fair market value of the house painting that I did. We are both required to report this income and pay any necessary taxes on it.
So, if you buy 5 BTC for $10 each, and then use the 5 BTC to buy something worth $50, then you don't have any capital gains income. The value of the BTC hasn't increased between the purchase of the BTC and the exchange for merchandise. You paid your income tax on the $50 when you earned it, before you bought the BTC. It is only when you hold those BTC long enough for them to increase in value that the IRS wants you to pay capital gains income tax on the increased value of the BTC.
Also, note that when you make a purchase of a new item from a business that resides in the same state as you (even over eBay), if your state has a sales tax (some states don't) that business is supposed to collect sales tax from you, report it, and pay it to the state. Not all businesses do this, but that doesn't mean that they aren't legally required to, it just means that they get away with tax evasion.
What surprises a lot of people is that if you purchase something from a business that does not reside in your state (mail order, phone order, internet order), even though that business does not collect the sales tax from you the law still requires that
you report the sale and pay a "use tax" directly to the state for the purchase. A whole lot of people aren't even aware that they are engaging in tax evasion when they don't do this.