php income twine reworking integer error

i have little financial concentration php front finish mysql behind end. i have ancient prejudices, i store income values mysql an integer cents. html forms grant quarrel dollar values, "156.64" i php modify cents following i store cents database.

i have duty both cleans dollar value form, translates cents. i frame streamer text, i frame trailing text, i greaten 100 modify an integer. final step is

$cents = (integer) ($dollars * 100);

this works glorious roughly everything, solely unequivocally few values '156.64' consistently translates 15663 cents. since does this?

if i this:

$cents = (integer) ($dollars * 100 + 0.5);

then consistently works. since i need supplement rounding value?

also, prejudices storing income amounts integers floating indicate values, longer needed? difficult boyant calculations furnish simply lifeless accurate income values adequate retaining 100% accurate accounting?