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	$56.27	6.332%	$59.833	$59.83	$59.85	$59.80
Purchase #2	$118.67	13.142%	$134.2656	$134.27	$134.25	$134.30
Purchase #3	$228.51	11.670%	$255.1771	$255.18	$255.20	$255.20
Purchase #4	$240.64	6.180%	$255.5116	$255.51	$255.50	$255.50
Purchase #5	$10.60	9.685%	$11.6266	$11.63	$11.65	$11.60
Purchase #6	$222.67	4.710%	$233.1578	$233.16	$233.15	$233.20
Purchase #7	$207.69	8.500%	$225.3437	$225.34	$225.35	$225.30
7 purchase totals =	$1,085.05		$1,174.9154	$1,174.92	$1,174.95	$1,174.90