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	$169.75	5.212%	$178.5974	$178.60	$178.60	$178.60
Purchase #2	$139.66	8.602%	$151.6736	$151.67	$151.65	$151.70
Purchase #3	$37.64	10.668%	$41.6554	$41.66	$41.65	$41.70
Purchase #4	$124.68	11.486%	$139.0007	$139.00	$139.00	$139.00
Purchase #5	$104.63	6.344%	$111.2677	$111.27	$111.25	$111.30
Purchase #6	$74.64	5.312%	$78.6049	$78.60	$78.60	$78.60
Purchase #7	$107.54	6.721%	$114.7678	$114.77	$114.75	$114.80
7 purchase totals =	$758.54		$815.5675	$815.57	$815.50	$815.70