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	$185.50	12.444%	$208.5836	$208.58	$208.60	$208.60
Purchase #2	$205.29	12.351%	$230.6454	$230.65	$230.65	$230.60
Purchase #3	$118.98	3.814%	$123.5179	$123.52	$123.50	$123.50
Purchase #4	$132.61	8.280%	$143.5901	$143.59	$143.60	$143.60
Purchase #5	$30.99	5.113%	$32.5745	$32.57	$32.55	$32.60
Purchase #6	$142.35	13.710%	$161.8662	$161.87	$161.85	$161.90
Purchase #7	$52.68	12.762%	$59.403	$59.40	$59.40	$59.40
7 purchase totals =	$868.40		$960.1807	$960.18	$960.15	$960.20