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	$93.48	6.309%	$99.3777	$99.38	$99.40	$99.40
Purchase #2	$222.58	8.490%	$241.477	$241.48	$241.50	$241.50
Purchase #3	$47.37	13.201%	$53.6233	$53.62	$53.60	$53.60
Purchase #4	$88.81	11.192%	$98.7496	$98.75	$98.75	$98.70
Purchase #5	$230.68	12.504%	$259.5242	$259.52	$259.50	$259.50
Purchase #6	$108.40	11.762%	$121.15	$121.15	$121.15	$121.20
Purchase #7	$222.85	3.783%	$231.2804	$231.28	$231.30	$231.30
7 purchase totals =	$1,014.17		$1,105.1822	$1,105.18	$1,105.20	$1,105.20