The only time I’ve ever really seen it happen is on cars that have auto stop/start, which essentially turn themselves off anyway.
Edit: Thanks for the answers everyone! I, in fact, did not know to begin with that it is called the tachometer and measured the revolutions of the engine and not the tires!
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As almost everyone else mentioned, the tachometer is measuring the engine speed–frequently the rotational speed of the crankshaft. Your speedometer is what measures your tire rotation (making an assumption of the tire’s radius). Most internal combustion engines will idle. This is mostly a legacy from when they used to use carburetors where they’d use a bit more fuel at start. Modern cars with electronic fuel injection don’t really have much of a penalty when starting the car; however, they will usually still idle.
Some newer cars will have a mode where they will shut off the engine when the car is stopped in order to avoid idling and save fuel. When you press the accelerator the car will automatically restart. In this case, the tachometer would read zero while the engine is off. I have driven one of these cars, and personally I dislike it. It is unnerving to me when the car isn’t idling, but then I still (deliberately) drive a manual transmission vehicle in the USA (for those elsewhere, almost all cars here are automatic).
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