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	$240.52	7.647%	$258.9126	$258.91	$258.90	$258.90
Purchase #2	$133.50	13.500%	$151.5225	$151.52	$151.50	$151.50
Purchase #3	$40.89	10.233%	$45.0743	$45.07	$45.05	$45.10
Purchase #4	$214.34	11.741%	$239.5057	$239.51	$239.50	$239.50
Purchase #5	$248.79	3.147%	$256.6194	$256.62	$256.60	$256.60
Purchase #6	$249.59	10.192%	$275.0282	$275.03	$275.05	$275.00
Purchase #7	$250.59	13.399%	$284.1666	$284.17	$284.15	$284.20
7 purchase totals =	$1,378.22		$1,510.8293	$1,510.83	$1,510.75	$1,510.80