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	$10.64	8.313%	$11.5245	$11.52	$11.50	$11.50
Purchase #2	$196.78	11.429%	$219.27	$219.27	$219.25	$219.30
Purchase #3	$59.72	9.186%	$65.2059	$65.21	$65.20	$65.20
Purchase #4	$118.61	11.280%	$131.9892	$131.99	$132.00	$132.00
Purchase #5	$141.71	6.631%	$151.1068	$151.11	$151.10	$151.10
Purchase #6	$170.35	6.715%	$181.789	$181.79	$181.80	$181.80
Purchase #7	$191.82	13.534%	$217.7809	$217.78	$217.80	$217.80
7 purchase totals =	$889.63		$978.6663	$978.67	$978.65	$978.70