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	$9.89	6.711%	$10.5537	$10.55	$10.55	$10.60
Purchase #2	$207.61	11.512%	$231.5101	$231.51	$231.50	$231.50
Purchase #3	$225.87	8.217%	$244.4297	$244.43	$244.45	$244.40
Purchase #4	$116.79	8.527%	$126.7487	$126.75	$126.75	$126.70
Purchase #5	$247.72	12.461%	$278.5884	$278.59	$278.60	$278.60
Purchase #6	$92.28	7.496%	$99.1973	$99.20	$99.20	$99.20
Purchase #7	$72.30	8.648%	$78.5525	$78.55	$78.55	$78.60
7 purchase totals =	$972.46		$1,069.5804	$1,069.58	$1,069.60	$1,069.60