Tom D
You could close your app programmatically using the Application.Current.Exit method: http://msdn.microsoft.com/en-us/library/ie/windows.ui.xaml.application.exit
Application.Current.Exit()
Note that it is in general not recommended to close a Store App like this though. The user is supposed to close it himself or it should be suspended: http://msdn.microsoft.com/en-us/library/windows/apps/hh465088.aspx
Please remember to mark helpful posts as answer to close the thread and then start a new one if you have a new question.