I haven't actually tested this om my T68 because I very very rarely get any notifications on it as I tend to treat it as an ereader first and foremost, but try tapping the area around the battery / wifi indicator on the top notification bar. This should bring up a settings menu in the lower right hand side of the screen.
The icon for settings is there, and I suspect that in case of any notifications, you should see an icon looking a bit like like a ladder, with three or four steps. Click on that and you can clear your notifications from the notifications bar. At least, that's how it works on my android phone and tablet so perhaps it has been carried over to out T68's.
Browsing the Google Play store I came upon this:
https://play.google.com/store/apps/d...ificationclear
Haven't tried it, but looks interesting if your intent is to manage notifications in detail.