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	$145.65	6.378%	$154.9396	$154.94	$154.95	$154.90
Purchase #2	$151.80	13.367%	$172.0911	$172.09	$172.10	$172.10
Purchase #3	$235.61	7.388%	$253.0169	$253.02	$253.00	$253.00
Purchase #4	$236.87	13.781%	$269.5131	$269.51	$269.50	$269.50
Purchase #5	$66.59	7.639%	$71.6768	$71.68	$71.70	$71.70
Purchase #6	$15.95	11.348%	$17.76	$17.76	$17.75	$17.80
Purchase #7	$151.30	6.297%	$160.8274	$160.83	$160.85	$160.80
7 purchase totals =	$1,003.77		$1,099.8249	$1,099.83	$1,099.85	$1,099.80