A few sources:

perlfaq4

sub round {
    my($number) = shift;
    return int($number + .5);
}
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perldoc -f int

int Returns the integer portion of EXPR. If EXPR is omitted, uses "$_". You should not use this function for rounding: one because it truncates towards "0", and two because machine representations of floating point numbers can sometimes produce counterintuitive results. For example, "int(-6.725/0.025)" produces -268 rather than the correct -269; that's because it's really more like -268.99999999999994315658 instead. Usually, the "sprintf", "printf", or the "POSIX::floor" and "POSIX::ceil" functions will serve you better than will int().