Update: Added "Perl6" tag to end of subject.

On my Debian 7, 64-bit system, with Perl 5.14 I see the following results

$ perl -e 'printf "13.24 rounds to %.*f0\n", 1, 13.24';
13.24 rounds to 13.20

$ perl -e 'printf "13.25 rounds to %.*f0\n", 1, 13.25';
13.25 rounds to 13.20

$ perl -e 'printf "13.26 rounds to %.*f0\n", 1, 13.26';
13.26 rounds to 13.30
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and using the Perl 6 REPL shows

> 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
[download]

which I believe is due at least partly to Perl 6's use of rational numbers--a major feature.