Apple - Wirelessly play audio from an iPad to a Mac

The AirServer application may offer the functionality that you're looking for. According to this 2011 review, the app can:

AirPlay is what lets you throw content from an iPad or iPhone wirelessly to speakers or your TV. To do this, you need to have an AirPort Express next to your speakers, or an Apple TV hooked up to your TV. Bluetooth speakers show up in the list, too. What you can’t do is beam movies from your iOS device direct to your big-screen iMac.

AirServer is a $3 app that adds in this last piece of the puzzle. With it running on your Mac, a new entry will show up in the AirPlay popover of any iOS device on the same network, as you’d expect.

Music just appears magically from your Mac’s speakers, or whatever speakers are hooked up to it. Movies open after a second in the Quicktime player, and it’s on-screen controls let you play, pause, scrub and change volume on the Mac itself.

According to the link on the AirServer website, the price for the current version (AirServer 4.0) is $14.99.

Another application with similar functionality is Banana TV. However, it doesn't support iOS 5, as this note on the app homepage states:

Banana TV has moved to free. We will not be supporting iOS5, although the latest build DOES support Lion. You need an iPhone or iPad running greater than or equal to iOS 4.2 and less than iOS 5.0. We apologize, but keeping up with Apple's continual change of the undocumented, private AirPlay interfaces just isn't something we can continue!

Both applications allow for media to be played from an iOS device to a networked Mac.

EDIT: Add current price of AirServer application.

How about Airfoil from Rogue Amoeba. It also offers the facility to receive audio from iOS devices and play out through your Mac. See this page for more details.

Airfoil Speakers can now receive audio from several new sources, without even needing to use Airfoil. What does that mean for you?

First and foremost, Airfoil Speakers for Mac can now receive audio from your iOS device! Launch Airfoil Speakers, and it will appear in the list of AirPlay devices on iOS. When you play audio in an app on your iPhone, iPod Touch, or iPad, you can select Airfoil Speakers from the AirPlay list, and you’ll hear the audio right on your Mac.