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. (a) The United States, its unincorporated agencies and instrumentalities;
2. (b) 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. (c) The American National Red Cross, its chapters and branches.