I don't see any problem with the multiplication (its quite rare for something that cannot evaluate to a number in PHP), though I do see bracket mismatching here. Guess I shouldn't have just cut and paste parts out of it:
Ok, that looks like its right. I initialized denom before the branch since it would otherwise become null outside in the event of a non-evaluation.
$valorPerc = 0;
if (0 < ($denom = $totaisOrdem[count($totaisOrdem)-2]['VLR']))
$valorPerc = ROUND((($totaisOrdem[count($totaisOrdem)-1]['VLR']/$denom)-1)*100,2);