Even not counting the old deer drive days, a surprising number of times. Not the majority mind you, but a solid 30% depending on how you define "need".
I've only ever had one that might not have expired a reasonable distance from the first shot. This one was due to a "weird" bullet performance combined with a deer that moved on the trigger break. This one took a snap shot on a running deer after a 200+ yard blood trail to anchor. I would have fired more the first time, but she was gone in the timber before I could cycle the bolt. I guess technically both shots were singles a good time apart, so a single shot firearm would have produced the same outcome. I have had a bunch that might have made it across a property line or into a very difficult area to retrieve without a second CNS shot. Despite popular rumor, they will often jump up and go through the woods even after a shoulder hit from a high powered rifle. The second one in the brainstem guarantees DRT. I've also had a few where I did not trust the first shot due to perceived target movement at the shot or the action of the animal/possible bullet deflection, and shot until they were down.
I've also put down a few known wounded deer for other hunters (I have a reputation as "the blood trail guy" and enjoy trailing a deer, so I'm often drafted for this duty) that required from 1 to 4 shots on the run while breaking cover before assuming abient temperature. I was quite proud of the neighbor's 10 pointer I put down across his hayfield even though it took me 3 rounds and the first 2 hits were shall we say less than perfect. Slowed him down a bunch though. Running offhand at 175-200 yards, I'll take it.