For the expose feature the knx integration there is a cooldown funcionality that will ensure that a value is not sent too often to the KNX bus. In addition to that many KNX devices offer an option to send a telegram only when the actual value has changed by some percentage (typical values are 3, 5 or 10).
This could be used in addition to cooldown to have better control / response times on changed values, but still not spam to bus too much with the same value all of the time.
Hi 
!
This could probably be done by exposing a helper/template entity doing the calculations (eg. rounding).
I think the approach has some pitfalls. Eg. if you have an outdoor temperature sensor that changes its value very frequently. With cooldown you can exactly control the max. frequency sent to the bus.
But with a value hysteresis you can’t really. It might look fine when you set it up at 15°C and set it to 5% difference → sending every 0,75°
Once winter comes and it gets around 0°C outside this will start spamming your Bus months after you set it up - probably without anyone monitoring it at this time.