It depends what kind of cartridge. A Barrett .50 will impart enough energy to penetrate the engine block of a car. Think about that. There are parts of a tank that are less armored than others...and in order to be assessed a "mission kill" you would have to destroy its ability to do its job, not necessarily to blow it into a million pieces. This could be separating the treads, killing one or more of the crew, destroying the optics...
It also is going to depend on what kind of tank. Most APC's will afford decent protection from RPGs and 7.62 AK-47 fire, but won't stop a .50 sniper rifle.