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	$138.89	13.367%	$157.4554	$157.46	$157.45	$157.50
Purchase #2	$226.52	4.223%	$236.0859	$236.09	$236.10	$236.10
Purchase #3	$217.56	7.487%	$233.8487	$233.85	$233.85	$233.80
Purchase #4	$81.76	8.608%	$88.7979	$88.80	$88.80	$88.80
Purchase #5	$145.25	6.325%	$154.4371	$154.44	$154.45	$154.40
Purchase #6	$214.54	13.514%	$243.5329	$243.53	$243.55	$243.50
Purchase #7	$102.90	8.366%	$111.5086	$111.51	$111.50	$111.50
7 purchase totals =	$1,127.42		$1,225.6665	$1,225.68	$1,225.70	$1,225.60