IIRC the -0.00 representation happens when you're using sprintf("%0.2f",$some_number_very_slighty_less_than_zero). The last two digits happen because they were specified in the format string. the minus sign is supposedly because that's how the C stdio lib does that.

update:

#include "stdio.h"

int main() {
  printf("%0.2f\n",-0.000000000000000000000000001);
}
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$ ./a.out 
-0.00
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