That's why you only use the least significant digits of any number that comes from a sensor. So if the temperature changes from 65.78614329 degrees to 66.24667

That's why you only use the least significant digits of any number that comes from a sensor. So if the temperature changes from 65.78614329 degrees to 66.24667182 degrees, you don't take 65 and 66, you take 329 and 182. Those digits are most likely to be random noise and not something an attacker can manipulate at will. Even if the analog part of the sensor is stuck at the same temperature as in your example, the digital reading will probably fluctuate around that value with plenty of random digits.