Solved!
Changing two lines in "func_display.php" and replacing "(int)" and "(int) round()" on lines 285 and 326, both to "number_format" with 2 decimals. And now percentages are more precise!

Original lines (285 and 326):
$howmuch_1 = ( int ) ( $value / $sum_total * 100 );
echo (int) round ($howmuch_3)."%";

Replaced lines (285 and 326):
$howmuch_1 = number_format (( $value / $sum_total * 100 ),2);
echo number_format($howmuch_3, 2)."%";

Hope this changes can help to someone 

Yeah, that change works too, but rounding percentages numbers always generate a little precision problem...

Some times percentages sum 99% and some other times 101%, depending on each rounding (and that's not good regarding to precision terms).

Even, with 2 decimals, precision goes from 99.99% to 100.01%... So, the best (but not recommended for most projects), is using 5 decimals.