Programming stepper motors to smoothly show value that is refreshed at certain intervals
car         VS.    meter
velocity           position
acceleration       velocity

So you need a trajectory planner for your meter so that it moves to the position (car velocity) with a certain velocity (car acceleration) with maximum motor acc/dec. As the meter will always lag  VS. the real value it won't cause jerky movement.
EDIT:
A simple digital RC filter
k=Tsample/RC, in your case Tsample is 180ms and RC shall be approx. 350ms, so k=0.51
k, input, y, y_old : float;

y = y_old + k*(input-y_old); 
y_old = y;

You do execute this at every received new value (each 180ms).