There are three main reasons to throw coins at Trevi:
to return to Rome one day.
to find love or romance in Rome.
to marry happily in Rome.
Of course, every wish needs its own coin. So, you will need two coins to find romance and to marry an Italian in Rome. If you have already found your love and want to return to Rome in the future, then just flip one coin. The coin’s denomination is not important, and it is not necessary to throw 2 euros. Believe me, 10 cents are enough.