How to track iTunes purchases on an Apple device

Our credit card statement came in with a charge to iTunes for $5.40. No one can seem to remember buying anything (two teens, two adults). Is there a way to trace charges from the different devices in our home? We have a Macbook Pro, an iPhone5, an iPad, and an iPod4. I tried looking at iTunes accounts on the iPod and the iPhone, but it doesn't say how much anything on the list cost, or when it was purchased/updated. Am I missing something obvious here? Thank you!!