So this is a strange one my wife noticed... A lot of the time the thermostat temp displayed on the thermostat itself doesn't match whats passed to hubitat... Here is a prime example... As you can see the thermostat says 67 degrees....
Does it match if you do a "Refresh"? The display is likely real-time, whereas it's possible it won't send a new report to the hub on every 0.1 degree change or whatever unless it is large enough or enough time has passed. I don't see any parameters to change this, and a quick look at one I have only shows historical reports to the hub of every whole degree (though maybe there is a way to change that...). So, my guess is a combination of this plus some rounded value (not necessarily rounded non-conventionally, given the above) on the display.
But I've never paid attention before this, so there could be more to the story...
Does your event history only show whole numbers on this for Hubitat like mine does? If so, that's the likely explanation (and those are likely rounded, despite the ".0" implying a significant figure...). This is with the stock driver, BTW, so things might be different with others.
The significant figure is more for Celsius. Thermostat natively is a Celsius device accurate to 0.5°C, driver handles the conversion behind the scenes.