This example comes from the supervising editor of the Straits Times, Sumiko Tan:
About €3,000 (S$6,000) are thrown into the [Trevi] fountain each day ... (Sunday Times Lifestyle, 31 May 2009).
Wrong. Since we aren’t counting each euro individually, but are thinking of €3,000 as a single sum, we need a singular verb:
About €3,000 is thrown into the [Trevi] fountain each day.