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	$172.31	7.365%	$185.0006	$185.00	$185.00	$185.00
Purchase #2	$217.38	6.523%	$231.5597	$231.56	$231.55	$231.60
Purchase #3	$218.37	5.576%	$230.5463	$230.55	$230.55	$230.50
Purchase #4	$70.60	8.353%	$76.4972	$76.50	$76.50	$76.50
Purchase #5	$37.73	10.158%	$41.5626	$41.56	$41.55	$41.60
Purchase #6	$190.85	12.176%	$214.0879	$214.09	$214.10	$214.10
Purchase #7	$39.55	5.293%	$41.6434	$41.64	$41.65	$41.60
7 purchase totals =	$946.79		$1,020.8977	$1,020.90	$1,020.90	$1,020.90