Description:
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PHP_ROUND_HALF_DOWN mode for round() doesn't work, it still increments last allowed decimal digit if next is larger than 4

Test script:
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var_dump(100 / 6);
var_dump(round(100 / 6, 4, PHP_ROUND_HALF_UP));
var_dump(round(100 / 6, 4, PHP_ROUND_HALF_DOWN));

Expected result:
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float 16.666666666667
float 16.6667
float 16.6666

Actual result:
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float 16.666666666667
float 16.6667
float 16.6667