Jaxx offers something called an HD or Hierarchical Deterministic wallet which uses your initial seed to generate new addresses each time you make a transaction. This is designed to increase privacy and was inspired by Bitcoin but creates a few usability quirks with the Ethereum account model and also tokens in Jaxx.
Either way you can always see your exact balance and which address it is sitting on by heading to your Tools section and clicking to Display Your Ethereum Keys. This view will show you all of your Ethereum addresses and the individual balances they hold. Incidentally you can also use these private keys to export the address to another wallet if required.
In regards to the IBAN this is a separate way that some wallets use to send funds and is designed to encourage adoption of Ethereum as a payment channel with the international code of XE as a prefix. Although it isn't widely in use right now, this would theoretically allow the Ethereum IBAN address to interact with the traditional banking system. You can read more about that here: