The daily buying rate of foreign currency which is determined by the Federal Reserve Bank of New York and certified to the Secretary of the Treasury in accordance with 31 U.S.C. 5151(e) shall be used for the conversion of foreign currency whenever a proclaimed rate or certified quarterly rate is not applicable under the provisions of §§ 159.33 and 159.34. If the date of exportation is one on which banks are generally closed in New York City, then the certified daily rate for the last preceding business day shall be considered the certified daily rate for the day of exportation.