For added security, you may like to turn on Apple's Guided Access feature on your iPad. This restricts access so that your staff can't access or download other apps on your iPad, keeping them focussed on serving your customers, rather than playing the latest games!
If you're not going to be on-site all the time, you may like to ensure your shift manager has access to the Guided Access PIN number in case any hardware like barcode scanners need to be re-paired with the Register app.
To turn on Guided Access, check out Apple's instructions here.