Well, you are acumulating rounding errors on every iteration.

Using a multiplication to calculate the current value from the beginning every time would probably improve the situation, though not solve it completely as 0.1 can not be represented as a floating point value.

for(my $i = 0; ; $i++) {
  my $v = $begin + $step * $i;
  last if $v > $end;
  print "$v\n";
}
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