There are exempted from the computation of the amount of the sales tax the gross receipts from the sale of any tangible personal property to:
1. The United States, its unincorporated agencies and instrumentalities.
2. Any incorporated agency or instrumentality of the United States wholly owned by the United States or by a corporation wholly owned by the United States.
3. The State of Nevada, its unincorporated agencies and instrumentalities.
4. Any county, city, district or other political subdivision of this State.