During climb your TAS is constantly increasing. ATC doesn't need a call every 5000 feet saying now we're going 270 knots, now we're going 290 knots, now we're going 320. The reg is average speed. At cruise that would be a change of 20+ knots. If the speed is just bouncing around your average isn't changing. If the turbulence is bad and you pull the power back to slow down 30 knots, then you should advise ATC.