voltage traces across pwm driven dc-motor: is that ok?
You can reduce Vce from 1.2V (on scope trace) to Vce=Vce(sat)=0.5V max


using the datasheet Vce(sat) =0.5V max with Ic/Ib=10 @ Ic=0.5A , do not use hFE.
thus change Rb from 560 Ohm to 50 Ohm or so for a load of 5 Ohm on 5V.  


more accurate KVL measurements can optimize this value.