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	$158.89	12.188%	$178.2555	$178.26	$178.25	$178.30
Purchase #2	$108.31	7.384%	$116.3076	$116.31	$116.30	$116.30
Purchase #3	$154.68	10.701%	$171.2323	$171.23	$171.25	$171.20
Purchase #4	$196.47	7.262%	$210.7377	$210.74	$210.75	$210.70
Purchase #5	$163.64	11.733%	$182.8399	$182.84	$182.85	$182.80
Purchase #6	$58.91	12.688%	$66.3845	$66.38	$66.40	$66.40
Purchase #7	$80.25	3.788%	$83.2899	$83.29	$83.30	$83.30
7 purchase totals =	$921.15		$1,009.0474	$1,009.05	$1,009.10	$1,009.00