Tweener Documentation
AS2 and AS3.
... rounded:value, ...
value:Boolean — Whether or not the values for this tweening must be rounded before being applied to their respective properties. This is useful, for example, when sliding objects that must be positioned on round pixels, like TextField instances that use pixel fonts; its x and y properties need to be rounded all the time to avoid blurring the text. It's also useful when tweening text on Flash Lite: since the current Flash Lite players render text with different space between each letter depending on the TextField position, individual letters seem to shake in relation to each other when moving text horizontally if you're not using rounded positions only. This option acts on all properties for that specific tween. The default value for this parameter (when omitted) is false.
// Slides a TextField to _x = 100, _y = 100, in 1 second, moving on rounded positions only (AS2)
Tweener.addTween(myTextField, {_x:100, _y:100, time:1, rounded:true});