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	$83.50	12.415%	$93.8665	$93.87	$93.85	$93.90
Purchase #2	$210.28	3.580%	$217.808	$217.81	$217.80	$217.80
Purchase #3	$223.44	13.276%	$253.1039	$253.10	$253.10	$253.10
Purchase #4	$148.46	4.340%	$154.9032	$154.90	$154.90	$154.90
Purchase #5	$239.89	13.509%	$272.2967	$272.30	$272.30	$272.30
Purchase #6	$50.90	9.232%	$55.5991	$55.60	$55.60	$55.60
Purchase #7	$216.47	12.211%	$242.9032	$242.90	$242.90	$242.90
7 purchase totals =	$1,172.94		$1,290.4806	$1,290.48	$1,290.45	$1,290.50