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	$53.93	4.841%	$56.5408	$56.54	$56.55	$56.50
Purchase #2	$90.49	4.536%	$94.5946	$94.59	$94.60	$94.60
Purchase #3	$20.88	7.168%	$22.3767	$22.38	$22.40	$22.40
Purchase #4	$52.57	6.248%	$55.8546	$55.85	$55.85	$55.90
Purchase #5	$77.55	4.733%	$81.2204	$81.22	$81.20	$81.20
Purchase #6	$25.49	13.547%	$28.9431	$28.94	$28.95	$28.90
Purchase #7	$126.77	7.643%	$136.459	$136.46	$136.45	$136.50
7 purchase totals =	$447.68		$475.9892	$475.98	$476.00	$476.00