使用PHP进行舍入问题

Question

Trying to overlay entries onto a PDF, however I'm having trouble on the extraction. The value of the entry is 2.914, but when I pull it through using

$dyed_ppg = $form_data['field']['12']);

It spits out 2.92 and rounded the number up. I've tried using

$dyed_ppg = number_format((float)$form_data['field']['12'], 4, '.', '');

But it outputs it as 2.9200

In SQL it is 2.914 so I'm not sure where the rounding is occuring...