Ironically, "-0.0" == 0 BUT triggers true in an ||... using that, however you CAN do...

$num = '-0.0000009';
$num = sprintf("%7.5f",$num);
$num = $num == 0 ? '0.00000' : $num;
print "$num\n";
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I was hoping || would work, cuz then you could do

$num = sprintf("%7.5f",$num) || '0.00000';
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but alas, no. The following works...

$num = sprintf("%7.5f",$num)+0 || '0.00000';
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but you lose all trailing zeros, which works if you only want to round, but not for formatting, so probably doesn't help.