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	$99.95	8.766%	$108.7116	$108.71	$108.70	$108.70
Purchase #2	$242.77	5.237%	$255.4839	$255.48	$255.50	$255.50
Purchase #3	$248.63	13.349%	$281.8196	$281.82	$281.80	$281.80
Purchase #4	$45.41	3.373%	$46.9417	$46.94	$46.95	$46.90
Purchase #5	$130.29	6.325%	$138.5308	$138.53	$138.55	$138.50
Purchase #6	$131.25	11.128%	$145.8555	$145.86	$145.85	$145.90
Purchase #7	$218.48	12.287%	$245.3246	$245.32	$245.30	$245.30
7 purchase totals =	$1,116.78		$1,222.6677	$1,222.66	$1,222.65	$1,222.60