Well, I would say that the number 5 is a rather arbitrary assignment, because there are sphincter muscles all along the the esophagus and intestines that support peristalsis, and one of the named 'sphincters' is not considered to be a true sphincter, but here are the officially named ones:
(1) Cardiac Sphincter, at the top of the stomach (this is the one that is not a true sphincter), separating the stomach from the esophagus.
(2) Iliac Sphincter , at the bottom of the stomach, separating the stomach from the small intestine.
(3) Ileocecal Valve separates the small intestine from the large intestine
(4) Involuntary Anal Sphincter, which is responsible for generating the urge to defecate.
(5) Voluntary Anal Sphincter, which allows one to control defecation.