I think there is a small typo in tivo's rule. I think the first condition in the 'if' statement should be Hall_temp - 1.0 and not Hall_temp +1.0. In the example above you want to get notified when the actual temp is less than 75.9 - 1 = 74.9 or above 75.9 + 1 = 76.9,
Edit: To get round numbers you'd have to initialize the Hall_Temp to a round number first (like 23.0), then the rule would only enunciate round numbers. However, it would still be possible to get off by a decimal. For instance, if your temp value is 23.0 and the actual temp goes from 23,1 to 22.9 then your new temp value would be with a .9. If your reporting device does not jump more than .1 then you should be OK and the round numbers will stay.