AS Noob alert! How to add easing to animation using AS?

I have a simple MC that I want scolling only when the mouse is over it. It’s a small banner animation but I don’t want it running constantly as it may get a little distracting.

Here’s a test of what I’m talking about.

Basically, I want to add some easing to the animation so that when you roll over / out the anim doesn’t stop dead, but gradually slows down.

This is my AS code that I have running on the MC:

on (release, rollOver) {
play();
}
on (release, rollOut) {
stop();
}

What would I need to add in order to get a nice easing happening?

TIA