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	$24.32	3.308%	$25.1245	$25.12	$25.10	$25.10
Purchase #2	$61.50	8.640%	$66.8136	$66.81	$66.80	$66.80
Purchase #3	$49.70	12.110%	$55.7187	$55.72	$55.70	$55.70
Purchase #4	$83.96	12.156%	$94.1662	$94.17	$94.15	$94.20
Purchase #5	$44.35	7.344%	$47.6071	$47.61	$47.60	$47.60
Purchase #6	$184.67	6.341%	$196.3799	$196.38	$196.40	$196.40
Purchase #7	$151.37	9.457%	$165.6851	$165.69	$165.70	$165.70
7 purchase totals =	$599.87		$651.4951	$651.50	$651.45	$651.50