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	$70.81	4.626%	$74.0857	$74.09	$74.10	$74.10
Purchase #2	$204.41	13.347%	$231.6926	$231.69	$231.70	$231.70
Purchase #3	$217.50	5.679%	$229.8518	$229.85	$229.85	$229.90
Purchase #4	$41.29	12.212%	$46.3323	$46.33	$46.35	$46.30
Purchase #5	$146.53	5.485%	$154.5672	$154.57	$154.55	$154.60
Purchase #6	$215.78	3.679%	$223.7185	$223.72	$223.70	$223.70
Purchase #7	$72.31	9.110%	$78.8974	$78.90	$78.90	$78.90
7 purchase totals =	$968.63		$1,039.1455	$1,039.15	$1,039.15	$1,039.20