Snapping parts to grid from external script?

What i want to do is have every part created snap to a grid of 2 studs for one, intergers only. Players themselves click on any spot to place a part, and the script snaps the part afterward. I know that i need to use the modulo operator for that, but it doesn't seem to help much.

I am able to snap the grid to intergers, but only to a grid of intergers. Here's my last out of many attempts with comments added:

workspace.ChildAdded:connect(function(child)
    print("New child added to Workspace")
    if child:IsA("Part") then
        print("Snapping child to grid")
        print("Original position: " .. child.Position.X .. " " .. child.Position.Y .. " " .. child.Position.Z)
        if child.Position.X > 0 then --If X is positive then...
            if child.Position.X % 2 ~= 0 then child.Position = Vector3.new(math.ceil(child.Position.X),child.Position.Y,child.Position.Z) end --Snap the part to an interger
            if child.Position.X % 2 ~= 0 then child.Position = Vector3.new(math.ceil(child.Position.X),child.Position.Y,child.Position.Z) end --Not divisible afterwards? Snap again.
        else --If it's negative then...
            if child.Position.X % -2 ~= 0 then child.Position = Vector3.new(math.floor(child.Position.X),child.Position.Y,child.Position.Z) end
            if child.Position.X % -2 ~= 0 then child.Position = Vector3.new(math.floor(child.Position.X),child.Position.Y,child.Position.Z) end
        end --If Z is negative then...
        --Ignore the lines about Y
        if child.Position.Y % 1 ~= 0 then child.Position = Vector3.new(child.Position.X,math.floor(child.Position.Y),child.Position.Z) end
        if child.Position.Y == 0 then child.Position = Vector3.new(child.Position.X,1,child.Position.Z) end
        if child.Position.Z > 0 then
            if child.Position.Z % 2 ~= 0 then child.Position = Vector3.new(child.Position.X,child.Position.Y,math.ceil(child.Position.Z)) end
            if child.Position.Z % 2 ~= 0 then child.Position = Vector3.new(child.Position.X,child.Position.Y,math.ceil(child.Position.Z)) end
        else
            if child.Position.Z % -2 ~= 0 then child.Position = Vector3.new(child.Position.X,child.Position.Y,math.floor(child.Position.Z)) end
            if child.Position.Z % -2 ~= 0 then child.Position = Vector3.new(child.Position.X,child.Position.Y,math.floor(child.Position.Z)) end
        end
        child.Position = Vector3.new(child.Position.X,child.Position.Y + 0.5,child.Position.Z)
        print("New position: " .. child.Position.X .. " " .. child.Position.Y .. " " .. child.Position.Z)
    else
        print("New child isn't a part - probably a player character")
    end
end)