I'd probably start with
float t = tempSens.getTempCByIndex(0)*10;
Then the main loop() would need an extra step to separate out the third digit.
Then I'd modify displayNumb() to take 3 arguments and use 3 shiftOut()s instead of two. It'd be good to make it also insert the dot in the right place (I think this is addressed through high bit of the middle digit).