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	$52.34	12.404%	$58.8323	$58.83	$58.85	$58.80
Purchase #2	$226.38	7.189%	$242.6545	$242.65	$242.65	$242.70
Purchase #3	$46.99	12.859%	$53.0324	$53.03	$53.05	$53.00
Purchase #4	$131.29	13.274%	$148.7174	$148.72	$148.70	$148.70
Purchase #5	$242.65	5.668%	$256.4034	$256.40	$256.40	$256.40
Purchase #6	$54.56	8.626%	$59.2663	$59.27	$59.25	$59.30
Purchase #7	$108.36	10.516%	$119.7551	$119.76	$119.75	$119.80
7 purchase totals =	$862.57		$938.6614	$938.66	$938.65	$938.70