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	$225.38	13.838%	$256.5681	$256.57	$256.55	$256.60
Purchase #2	$89.82	6.565%	$95.7167	$95.72	$95.70	$95.70
Purchase #3	$204.89	8.821%	$222.9633	$222.96	$222.95	$223.00
Purchase #4	$62.28	5.541%	$65.7309	$65.73	$65.75	$65.70
Purchase #5	$220.34	4.675%	$230.6409	$230.64	$230.65	$230.60
Purchase #6	$196.88	10.642%	$217.832	$217.83	$217.85	$217.80
Purchase #7	$179.52	11.511%	$200.1845	$200.18	$200.20	$200.20
7 purchase totals =	$1,179.11		$1,289.6364	$1,289.63	$1,289.65	$1,289.60