Keep in mind that the money in your account and the prices of the products are technically in BTC. There's an option to display USD in the interface for your convenience, but everything behind the scenes happens in BTC. So, it may be that when a vendor pegs the price to a USD value, the site recalculates the price on a schedule which is not the same as the exchange rate update. For example, a vendor pegs a product to $100. Exchange rate is $90 at that time, so the BTC value is set to 1.11 BTC. Several hours later, SR updates its exchange rate from the MtGox average to $92 but hasn't recalculated all listings yet. You look at the product, which is 1.11 BTC, but because your changed the display option to USD, it shows up as 1.11 * $92 (the new rate) = $102.12. That's probably why so many listings have weird prices down to random cent amounts. What vendor would peg a product to a price like that?