using UnityEngine;
using System.Collections;

public class Jumping : MonoBehaviour { public GameObject nissan350z;

    private int tmpScore = 0;

    // Update is called once per frame
    void Update () {
       if(Input.GetKey("1"))
       {
           transform.Rotate(Vector3.forward * (100*Mathf.PI) * Time.deltaTime);
         tmpScore += 5;
        }
        if(Input.GetKey("2"))
        {
           transform.Rotate(Vector3.up * (100*Mathf.PI) * Time.deltaTime);
         tmpScore += 10;
        }
        if(Input.GetKey("3"))
        {
              transform.Rotate(Vector3.down * (100*Mathf.PI) * Time.deltaTime);
         tmpScore += 15;
        }
        if(Input.GetKey("4"))
        {
           transform.Rotate(Vector3.left * (100*Mathf.PI) * Time.deltaTime);
         tmpScore += 20;
        }
        if(Input.GetKey("5"))
        {
              transform.Rotate(Vector3.right * (100*Mathf.PI) * Time.deltaTime);
         tmpScore += 25;
        }
    }

}

This code will add 5,10,15,20,25 relative to the number keys pressed (1,2,3,4,5) to a tmpScore variable. Now what you need is a way to determine if the car has landed properly... This could be done with colliders/triggers under the car or through a more complicated script. Once the car has landed properly you will need to add the tmpScore to the current score of your player.

score += tmpScore

I will need more information about the game (Probably need to see a live demo) in order to figure out which solution would be best for checking if the car lands properly.