1989, Isaac Levy, translator, The Pentateuch (translation of, Samson Raphael Hirsch, Der Pentateuch, ubersetzt und erlautert), second edition, volume 2, Exodus, Judaica Press, →ISBN, page 582 (commentary to Exodus 30:16), Owing to the enormous number of half-shekel coins required each year in Adar, these were greatly in demand, and the money-changers made a small fixed charge of an agio for changing whole into half shekels.
Source: wiktionary