In theory, no. 8cm of armour, sloped at 20-30 degrees, is going to be better than the 60-70mm of penetration capability at 30 degrees of the M61 APC and M72 AP rounds.
In practice, yes.
The problem is that too many folks treat anti-tank gunnery as a game of Top Trumps. They look at value #1 (armor), compare it to value #2 (penetration statistics), and conclude that whichever value is higher will win. Real life, of course, is not that, and it is not necessary to penetrate armor to kill a tank. To an army, "kill" is as good as "destroy", at least as long as the battle is ongoing.
For example, the Sherman may choose to shoot at the KT's tracks. If the KT gets immobilised, it is not unusual for the crew to bail out., fearing that they will be easy targets for something with a bigger gun which may be next, or simply getting swarmed by infantry. There has been precedent of the M4 firing smoke rounds at heavily armoured tanks: The white phosphorous either will convince the crew the tank is on fire and they'll get out, or it might leak down through the engine grilles and actually start the tank on fire. Note that the reason we still have a running Tiger in the world is because its turret got jammed by a 6-pounder shell to which the tank should be, on paper, impervious. Or just pummel the thing into submission: One Tiger crew was found to have expired from concussion after being battered by dozens of HE rounds. The mechanisms inside the tank wouldn't like it either.
And, of course, there's the Golden BB. I have found one instance of an entire company of M3 Stuarts taking on a Tiger I, which their 37mm guns shouldn't be able to defeat, in North Africa. They eventually peppered the thing so many times that something broke through somewhere, and lucky is as good as skill or technology if the final result is the same. That golden BB could be an unknown weak point in the armor plate due to a metallurgical flaw, maybe a tiny designed feature like a thermal exhaust port, or some other thing which just got it right.
It wouldn't be easy, and it would take a ballsy tank crew (or more likely, crews, as US tanks tended not to go around on their own) to do it, but it could be done. Of course, the better move is to just call up a 76mm tank which, by the time folks were meeting King Tigers, wouldn't have been that hard to come across.
The sides are actually easier to pierce than the back, in the King Tiger's case. In Soviet trials, the Sherman was capable of penetrating the 82 mm side armour of a regular Tiger from up to 625 meters. The side armour of a King Tiger is only 80 mm. Provided the Sherman scored a lucky hit under the pannier without the shell hitting the wheels, it would be able to penetrate.
In British trials, a strike with an HE shell underneath the Tiger's pannier split the welds and blew out the pannier floor. Had any ammunition been present, it would have likely exploded. The King Tiger was vulnerable in a similar fashion. Unfortunately, I don't have any live fire British trials against the King Tiger, so we cannot know for sure. Examination of captured King Tigers showed that they might have been vulnerable to 75 mm HEAT in certain areas, but I don't know if the British ever tried.
P. Samsonov Sherman vs. Tiger
Armour Branch Report on Firing Trial against German Tiger Pz.Kw.VI
Armour Branch Report on Armour Quality & Vulnerability of «Tiger» II Turret