Is it cheaper to keep the AC at one temp?

I was talking to my roommate, who said she had heard that it ends up actually being cheaper to keep the AC at one consistent temp as opposed to bumping the temp higher during the day. I can see how this would keep the unit from running as much if someone were to keep their thermostat at, say, 75°. However, we run warm and tend to set our thermostat to 68° at night, and have been setting it at 74° during the day for the dog. Wondering if anyone who has more expertise has thoughts on this?