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	$11.57	13.318%	$13.1109	$13.11	$13.10	$13.10
Purchase #2	$229.76	10.341%	$253.5195	$253.52	$253.50	$253.50
Purchase #3	$121.25	7.727%	$130.619	$130.62	$130.60	$130.60
Purchase #4	$109.57	9.362%	$119.8279	$119.83	$119.85	$119.80
Purchase #5	$103.94	13.683%	$118.1621	$118.16	$118.15	$118.20
Purchase #6	$111.58	13.283%	$126.4012	$126.40	$126.40	$126.40
Purchase #7	$94.55	6.531%	$100.7251	$100.73	$100.75	$100.70
7 purchase totals =	$782.22		$862.3657	$862.37	$862.35	$862.30