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	$99.48	4.261%	$103.7188	$103.72	$103.70	$103.70
Purchase #2	$107.40	3.510%	$111.1697	$111.17	$111.15	$111.20
Purchase #3	$224.89	12.763%	$253.5927	$253.59	$253.60	$253.60
Purchase #4	$186.52	7.249%	$200.0408	$200.04	$200.05	$200.00
Purchase #5	$248.53	10.741%	$275.2246	$275.22	$275.20	$275.20
Purchase #6	$86.80	13.737%	$98.7237	$98.72	$98.70	$98.70
Purchase #7	$161.98	8.757%	$176.1646	$176.16	$176.15	$176.20
7 purchase totals =	$1,115.60		$1,218.6349	$1,218.62	$1,218.55	$1,218.60