In cb, you indicated that the general problem is to do a Banker's Round, where /\d5/ is rounded to the even digit. I think you want to work with the string representation of the number for this, so that machine numbers don't interfere with the rules.

# handle 5 in the thousandth's place with nothing or zeros following
$pete =~ s/(        # substitute, start capture $1
            \d*     # none or more digits
            \.      # a decimal point
            \d      # tenths digit
           (\d)     # capture hundredths digit as $2
           )        # end capture $1
           50*$     # digit 5 followed by none or more 0's to the end
          /1&$2 ? $1+.01 : $1/xe;
# then do as you had
$rooker = sprintf "%.2f", $pete;
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By handling the special case as a string before the numeric round, we avoid binary-meets-decimal conflicts.

After Compline,
Zaxo