The cost of mailing a letter weighing up to an ounce in the United States was 10 cents from March 2, 1974 through Dec. 31, 1975, according to the United States Postal Service. Postcards required 10 cents of postage from May 29, 1978 to March 22, 1981.
For Canadian collectors, the 10-cent stamp had a longer life. It was the rate to send up to an ounce to the United States from Jan. 1, 1972 to March 1, 1977. Postcards were mailed within Canada for a dime from Sept. 1, 1976 to March 1, 1977, according to the Canadian Philately website. Third class mail, which included greeting cards, was 10 cents from March 1, 1977 to April 1, 1978.