Let ME talk about overcomplicating stuff…
Take a look at the expression below. It converts the rotation value, makes it a String, and evaluates if it has just one character to add a “0” accordingly.
That should help while somebody smarter thinks something simpler.
needleRot = Math.floor((thisComp.layer("needle wiggle").transform.rotation)/4.5) * 0.1
needleRot = needleRot.toString();
if (needleRot.length == 1){
needleRot + ".0";
} else {
needleRot;
}