How to correct (round) the size value?

You want to resize the artboards? Or the actual artwork inside the document? For now I'll assume you want to adjust the artboard since resizing the artwork can be much trickier depending on it's composition. Here's a function that will resize all the artboards to the closest integer.

function resizeArtboards()
{
    if(app.documents.length > 0)
    {
        var docRef = app.activeDocument;
        var aB = docRef.artboards;
        //loop each artboard
        for(var a=0;a<aB.length;a++)
        {
            var thisAb = aB;
            //get the width and height of this artboard
            var rect = thisAb.artboardRect;
            var w = Math.round(rect[2] - rect[0]);
            var h = Math.round(rect[1] - rect[3]);
            //set the dimensions of this artboard to the rounded size
            var newDim = [rect[0],rect[1],rect[0] + w, rect[1] - h];
            thisAb.artboardRect = newDim;
        }
    }
    else
    {
        alert("You must have a document open.");
    }
}
resizeArtboards();