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	$54.89	8.511%	$59.5617	$59.56	$59.55	$59.60
Purchase #2	$228.46	11.509%	$254.7535	$254.75	$254.75	$254.80
Purchase #3	$112.50	4.760%	$117.855	$117.86	$117.85	$117.90
Purchase #4	$240.56	6.301%	$255.7177	$255.72	$255.70	$255.70
Purchase #5	$37.51	5.367%	$39.5232	$39.52	$39.50	$39.50
Purchase #6	$18.99	6.473%	$20.2192	$20.22	$20.20	$20.20
Purchase #7	$162.25	8.570%	$176.1548	$176.15	$176.15	$176.20
7 purchase totals =	$855.16		$923.7851	$923.78	$923.70	$923.90