Very low temperature (-25C) on ds18b20 precision
The error is guaranteed to be within +/-2 degrees C over the useful range.

 

That (and only that) is what you can depend on. If that's not accurate enough, use another sensor or adjust the reading with individual per-sensor calibration (not usually a good way to go if you have any option at all because giving up interchangeability means you can't just replace parts in the field).  

An advantage of this type of sensor is that the error guarantee of this mixed-signal digital-output part pretty much includes the entire system error. Using analog sensors such as an RTD would require signal conditioning and the evaluation of the total system accuracy will involve a bunch of engineering calculations. The sensor error of a Class A Pt-RTD is about +/-0.2 degrees C at your target temperature. 

If +/-2 degrees C is good enough (probably you just need to guarantee the maximum storage temperature) then maybe it's an acceptable sensor, though it makes sense that the energy cost of maintaining a given maximum temperature with error +/-2 degrees C will be ~3% higher than if you can measure the temperature to within +/-0.5 degrees C (assuming Newtonian heat transfer and average Ta of 25 degrees C).