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s/\.[0-9]\K(?:[0-4]|([5-9]))/$1?5:0/e
s{\.[0-9]\K([0-9])}{int($1/5)*5}e;
s{(.*)}{sprintf("%.2f", int($1*20)/20)}e;
$_ = sprintf("%.2f", int($_*20)/20) . /(?!)/; # oblig regex