The answer, from the United States Court of Appeals for the Fifth Circuit, is this:
[T]he concern of Congress with the immorality, inefficiency, and unethical character of bribery presumably does not vanish simply because the tainted payments are intended to secure a favorable decision less significant than winning a contract bid. Obviously, a commercial concern that bribes a foreign government official to award a construction, supply, or services contract violates the statute. Yet, there is little difference between this example and that of a corporation’s lawfully obtaining a contract from an honest official or agency by submitting the lowest bid, and —— either before or after doing so —— bribing a different government official to reduce taxes and thereby ensure that the under-bid venture is nevertheless profitable. Avoiding or lowering taxes reduces operating costs and thus increases profit margins, thereby freeing up funds that the business is otherwise legally obligated to expend. And this, in turn, enables it to take any number of actions to the disadvantage of competitors. Bribing foreign officials to lower taxes and customs duties certainly can provide an unfair advantage over competitors and thereby be of assistance to the payor in obtaining or retaining business.
View the Fifth Circuit's Opinion here.