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	$203.68	11.165%	$226.4209	$226.42	$226.40	$226.40
Purchase #2	$225.93	3.361%	$233.5235	$233.52	$233.50	$233.50
Purchase #3	$52.60	4.278%	$54.8502	$54.85	$54.85	$54.90
Purchase #4	$103.86	4.677%	$108.7175	$108.72	$108.70	$108.70
Purchase #5	$104.93	6.283%	$111.5228	$111.52	$111.50	$111.50
Purchase #6	$69.77	11.192%	$77.5787	$77.58	$77.60	$77.60
Purchase #7	$13.51	5.412%	$14.2412	$14.24	$14.25	$14.20
7 purchase totals =	$774.28		$826.8548	$826.85	$826.80	$826.80