> say sprintf("13.24 rounds to %.*f0", 1, 13.24);
13.24 rounds to 13.20

> say sprintf("13.25 rounds to %.*f0", 1, 13.25);
13.25 rounds to 13.30

> say sprintf("13.26 rounds to %.*f0", 1, 13.26);
13.26 rounds to 13.30