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	$126.72	7.506%	$136.2316	$136.23	$136.25	$136.20
Purchase #2	$111.35	7.422%	$119.6144	$119.61	$119.60	$119.60
Purchase #3	$154.45	11.837%	$172.7322	$172.73	$172.75	$172.70
Purchase #4	$211.85	4.700%	$221.807	$221.81	$221.80	$221.80
Purchase #5	$225.65	7.554%	$242.6956	$242.70	$242.70	$242.70
Purchase #6	$7.87	11.463%	$8.7721	$8.77	$8.75	$8.80
Purchase #7	$81.71	9.684%	$89.6228	$89.62	$89.60	$89.60
7 purchase totals =	$919.60		$991.4757	$991.47	$991.45	$991.40