The problem is NOT that printf is stupid.
Yes, if you implement your own "round to 2 decimal places" algorithm that doesn't actually round but instead truncates, then you'll (often) get a different answer than if you actually round (whether or not you use sprintf to actually round, which is one of the better choices available).
Specifically round arithmetically using your own rules and you should at least get consistent results.
See, that just proves that you didn't learn the lesson that a bunch of the other replies in this thread were trying to teach.
sub consistentlyRound {
my( $w ) = @_;
my $p = int( ($w+0.005)*100 );
return $p/100;
}
my $x = 0.015;
my $y = 0.0001;
$y += 0.0001 for 1..149;
print "x=$x y=$y\n";
printf "x~%.2f y~%.2f (stupid printf rounding)\n", $x, $y;
$x = consistentlyRound( $x );
$y = consistentlyRound( $y );
print "x~$x y~$y (consistent arithmetic rounding)\n";
__END__
x=0.015 y=0.015
x~0.01 y~0.01 (stupid printf rounding)
x~0.02 y~0.01 (consistent arithmetic rounding)
It is just that your arithmetic adds more floating point operations that can change the inconsistency! I can find cases where your particular arithmetic happens to be more consistent than sprintf's. Above I show a case where sprintf() is more consistent.
Now go read the other replies and/or what they link to more carefully and learn why.
Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
Read Where should I post X? if you're not absolutely sure you're posting in the right place.
Please read these before you post! —
Posts may use any of the Perl Monks Approved HTML tags:
 a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

For: 

Use: 
 &   & 
 <   < 
 >   > 
 [   [ 
 ]   ] 
Link using PerlMonks shortcuts! What shortcuts can I use for linking?
See Writeup Formatting Tips and other pages linked from there for more info.

