5. Exceptions from examination in the classified customs service are hereby made as follows:
(a) Deputy collectors who do not also act as inspectors, examiners, or clerks.
(b) Cashier of the collector.
(c) Assistant cashier of the collector.
(d) Auditor of the collector.
(e) Chief acting disbursing officer.
(f) Deputy naval officers.
(g) Deputy surveyors.
(h) One private secretary or one confidential clerk of each nominating officer.
(i) Any person appointed to a position which requires only a portion of his time and attention for the performance of its duties, pays him a compensation not exceeding $300 per annum, and permits of his pursuing other regular business or occupation, such person being conveniently located for the performance of said duties.