private float scrollStep, closestPosition = 0.0f;

private int elementCount = 3;

​

private void Start()

{

    this.scrollStep = 1.0f / this.elementCount;

}

​

private void Update()

{

    if (!Input.GetMouseButton(0)) 

    {

        this.scroll.normalizedPosition = Mathf.Lerp(this.scroll.normalizedPosition, this.closestPosition, )

    }

    else

    {

        this.closestPosition = this.scroll.normalizedPosition;

        for (var i = 0; i < this.elementCount; i++)

        {

            if (this.scroll.normalizedPosition > i * this.scrollStep)

            {

                this.closestPosition = i * this.scrollStep;

            }

        }

    }

}