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	$9.29	8.606%	$10.0895	$10.09	$10.10	$10.10
Purchase #2	$85.87	6.749%	$91.6654	$91.67	$91.65	$91.70
Purchase #3	$55.35	11.831%	$61.8985	$61.90	$61.90	$61.90
Purchase #4	$212.60	5.792%	$224.9138	$224.91	$224.90	$224.90
Purchase #5	$54.30	13.513%	$61.6376	$61.64	$61.65	$61.60
Purchase #6	$87.46	9.488%	$95.7582	$95.76	$95.75	$95.80
Purchase #7	$188.70	4.113%	$196.4612	$196.46	$196.45	$196.50
7 purchase totals =	$693.57		$742.4242	$742.43	$742.40	$742.50