Not required. Sometimes towers want to know when your clear their
airspace, sometimes they don't care.

Yeah, I used to tell Class D towers when I was clear all the time, till a
controller somewhat sarcastically responded "Uh, okay niner-niner-three."

From his tone of voice it was obvious that he really didn't care (and was,
in fact, somewhat annoyed that I called him), so I no longer bother.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"