26 CFR § 49.4264(e)-1 - Round trips.
(a)In general. For purposes of the regulations in this subpart, a round trip shall be considered to consist of two separate trips, i.e., one trip from the point of departure to the destination and a second trip in returning from the destination. A round trip includes certain journeys in which the same routing is not followed on the return trip from the destination to the point of departure as was taken on the going trip (sometimes referred to as “circle trips”). In the case of a cruise or tour (i.e., transportation to no set destination but with one or more intermediate stops en route) the point farthest from the point of departure will be regarded as the destination for purposes of applying the term “round trip”. If a cruise or tour ends at a point other than the one at which it began, the rules of “open jaw” transportation set forth in paragraph (b) of this section apply.
(b)Open jaw transportation. Transportation which qualifies under this paragraph as “open jaw” transportation will be treated in the same manner as a round trip. For purposes of the regulations in this subpart, “open jaw” transportation means (1) transportation from the point of departure to a specified destination and return from the specified destination to a point other than the original point of departure, or (2) transportation from the point of departure to a specified destination and return from a point other than the specified destination to the original point of departure, provided that where the points of the open jaw are within the continental United States or the 225-mile zone, the distance between the points of the open jaw does not exceed the distance of the shorter segment traveled. For example, a trip from New York to New Orleans via Panama would be considered as one trip from New York to Panama and separate trip from Panama to New Orleans, since the distance between the points of the open jaw (i.e., New York and New Orleans) is shorter than the distance between Panama and New Orleans (the shorter of the two segments traveled). Both trips would be nontaxable. On the other hand, transportation from New York to Miami via Bermuda does not qualify as “open jaw” transportation (since the points of the open jaw are in the United States and the distance between them is greater than the shorter segment traveled) and therefore would be considered a single trip from New York to Miami and would be taxable.