想定スクリーンの高さからカメラを拡大・縮小し、想定スクリーンサイズをドット絵の１ドットと一致させるver

PixelBase.cs

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class PixelBase : MonoBehaviour {

	void LateUpdate () 
	{
		Vector3 cashPosition, cashScale;

		cashPosition = transform.localPosition;
		cashScale = transform.localScale;
		transform.localPosition = new Vector3( 
		                Mathf.RoundToInt( cashPosition.x),
		                Mathf.RoundToInt( cashPosition.y),
		                Mathf.RoundToInt( cashPosition.z));
		                
		transform.localScale = new Vector3(
					Mathf.RoundToInt( cashScale.x),
					Mathf.RoundToInt( cashScale.y),
					Mathf.RoundToInt( cashScale.z));
	}
}

ResizeByPixel.cs

using UnityEngine;
using System.Collections;

public class ResizeByPixel : MonoBehaviour 
{
	public int pixelSize;
	public float defaultSize = 1;

	public int screenHeight =  1920;

	void OnValidate()
	{
		float orthographicSize = screenHeight / pixelSize * 0.5f;
		Camera.main.orthographicSize = orthographicSize;

		defaultSize = Mathf.Max(0.0001f, defaultSize);

		if( pixelSize < 1 )
			return;
		float rate = defaultSize / pixelSize;
		transform.localScale = new Vector3(rate, rate, rate);
	}
}