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	$6.37	11.255%	$7.0869	$7.09	$7.10	$7.10
Purchase #2	$146.95	10.185%	$161.9169	$161.92	$161.90	$161.90
Purchase #3	$56.57	8.770%	$61.5312	$61.53	$61.55	$61.50
Purchase #4	$86.81	4.437%	$90.6618	$90.66	$90.65	$90.70
Purchase #5	$52.66	4.845%	$55.2114	$55.21	$55.20	$55.20
Purchase #6	$239.97	6.711%	$256.0744	$256.07	$256.05	$256.10
Purchase #7	$89.91	11.320%	$100.0878	$100.09	$100.10	$100.10
7 purchase totals =	$679.24		$732.5704	$732.57	$732.55	$732.60