Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$20.45	3.482%	$21.1621	$21.16	$21.15	$21.20
Purchase #2	$240.31	13.397%	$272.5043	$272.50	$272.50	$272.50
Purchase #3	$191.75	4.509%	$200.396	$200.40	$200.40	$200.40
Purchase #4	$189.59	9.874%	$208.3101	$208.31	$208.30	$208.30
Purchase #5	$76.91	7.613%	$82.7652	$82.77	$82.75	$82.80
Purchase #6	$104.52	12.746%	$117.8421	$117.84	$117.85	$117.80
Purchase #7	$194.67	8.148%	$210.5317	$210.53	$210.55	$210.50
7 purchase totals =	$1,018.20		$1,113.5115	$1,113.51	$1,113.50	$1,113.50