Rounding transform.position? With parents

How do I round my object(a buildable), to the nearest say .25, .5 or 1(does not matter which), in position(x,y,z), and the rotation to the nearest 30 degrees, I know this could be achieved with Mathf.Round() but how do I make it that it does not mess up the local position/rotation. It is a buildable which is a gameobject that in in a fp controller("Main Camera/Tools/TheObject" to be exact). It also has a move up/down command, which also I need help making it work with the global position.

So I guess the main question is how do I make the global position/rotation round, without messing up the local position/rotation.

I guess another way to word this is: The local position is 0,0,0 and the global is not known, the local rotation is -90,0,0 and global is not known, how would I round the global without messing up the local, and still having the object infront a play, but with a rounded transform.

Code(if needed):

 using UnityEngine;
 using System.Collections;
 
 public class Buildable : MonoBehaviour {
 
     public PlayerItemManager itemManager;
 
     private float holdTimer = 0;
 
     public float objectYPosOffset = 0;
 
     void Start(){
         itemManager = transform.root.GetComponent<PlayerItemManager> ();
         objectYPosOffset = -2.3f;
     }
 
     void OnEnable(){
         itemManager = transform.root.GetComponent<PlayerItemManager> ();
         objectYPosOffset = -2.3f;
     }
 
     void Update(){
         ManageInput ();
         RoundObjectTransform ();
         ManageBuilding ();
     }
 
     private void ManageInput(){
         if (Input.GetKeyUp (KeyCode.PageUp)) {
             objectYPosOffset += 0.25f;
         }
         if (Input.GetKeyUp (KeyCode.PageDown)) {
             objectYPosOffset -= 0.25f;
         }
     }
 
     private void ManageBuilding(){
         if (Input.GetMouseButton (1)) {
             holdTimer+=Time.deltaTime;
             if(holdTimer > 1){
             holdTimer = 0;
             RoundObjectTransform();
             PlaceObject();
             }
         }
     }
 
     private void RoundObjectTransform(){
         Vector3 pos = transform.localPosition;
         pos.y = 1 + objectYPosOffset;
         transform.localPosition = pos;
         Vector3 rot = transform.eulerAngles;
         rot.x = -90;
         transform.eulerAngles = rot;
         //transform.rotation.x = -90;
     }
 
     private void PlaceObject(){
         GameObject go = Resources.Load ("Buildables/"+gameObject.name) as GameObject;
         GameObject obj = Network.Instantiate (go,transform.position,transform.rotation,0) as GameObject;
         itemManager.UseCurrentSlot (true);
 
     }
 
 }