Here's my variant. It serves the same purpose, but gives rounder numbers for large inputs.

sub fuzz {
    my $x = int($_[0]);
    0 == $x and return 0;
    my $sgn = $x < 0 ? ($x = - $x, -1) : 1;
    my $ten = 0; 
    while (10 <= $x) { $x = $x/10; $ten++; }
    my $y = 
        $x <= 1.25 ? 1 :
        $x <= 2 ? 1.6 :
        $x <= 3.1 ? 2.5 :
        $x <= 5 ? 4 :
        $x <= 8 ? 6.3 :
        10;
    $sgn * int(0.6 + $y * 10 ** $ten);
}
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