This would make sense if "100000.0" was printed as 1e05

Yes - I, too, would prefer to see the same rule applied to both leading and trailing zeroes. Unfortunately, that's not the way it's being done. Another way of avoiding the scientific notation (no matter how many leading zeroes) is to convert to a Math::BigFloat object:

perl -MMath::BigFloat -wle "print Math::BigFloat->new(1e-10)"
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(Replace double quotes with single quotes on nix.)

Cheers,
Rob