Couple of pieces of advice:

• Stop parsing delimited strings by hand. You can use Text::CSV
even for something with a different separator as the perldoc says, "The module accepts either strings or files as input and can utilize any user-specified characters as delimiters, separators, and escapes so it is perhaps better called ASV (anything separated values) rather than just CSV.'
• Try perldoc -q switch instead of those if statements.
• For your question, provided you have an ordered set of times, I would quantize them to multiples of five and then aggregate them in a hash. For instance:

  linux~> perl -e 'my @quant = (); my @times = qw|12 14 21 27 30|; sub r
  +ound{while (@_[0]%5 != 0){@_[0]++}; return @_[0]}; for(@times){print 
  +round($_), qq|\n|};'
  [download]