$content =~ s/(\d\d\.\d*)/sprintf("%.6f",$1);/ge; #round to 6 decimal 
+digits
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One can avoid hard-coding the rounding precision by using either
    my $n = $some_integer;
    ... sprintf("%.${n}f", $1) ...
or the "wildcard" (if that's the right term (update: maybe "placeholder"?)) format specifier
    ... sprintf('%.*f', $n, $1) ...

Update: In the code above, I've implied that  $n must be an integer. Interestingly (for some definition of "interesting"), if it is not, then the first code example ($n interpolated) screws up, but the second (* wildcard specifier) behaves "properly", DWIMishly ignoring the fractional part of the numeric value. (I haven't checked yet to see if this behavior is the same as in C/C++/D/etc.)