Square has a new iPad app called Square Register, which it deems “everything you need to start, run and grow your business all in one free iPad app.” That’s a bold promise. Can it deliver?

Well, lots of businesses are already pretty high on Square itself. In December, the company announced that a million merchants are using the service. That number has likely increased significantly since then. According to AllThingsD, the company is processing $4 million a year.

So what’s in the app?

If you sign up, you’ll get the free card reader mailed to you. You can organize items and create a custom inventory. It includes fast checkout via “favorites,” and the 2.75% per swipe (Visa/Master Card/Discover/AmEx) rate. You can create a loyalty program. You can create and publish your profile to the Square Directory.

There are analytics features with interactive charts and employee permissions. You can set custom gratuity amounts to appear at the end of a purchase flow, and personalise receipts (while letting customers decide between paper, text or email). You can wirelessly print receipts or open your cash drawer.

The app works with any iPad running iOS 5.

As iPads continue to gain adoption, particularly among small businesses, this app will no doubt be appealing to plenty of merchants. Another big boost for Square should be coming as it gets integrated into taxi cabs around New York City. Even the president’s campaign is taking advantage of the service.