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	$241.42	6.389%	$256.8443	$256.84	$256.85	$256.80
Purchase #2	$210.41	6.428%	$223.9352	$223.94	$223.95	$223.90
Purchase #3	$9.98	5.349%	$10.5138	$10.51	$10.50	$10.50
Purchase #4	$14.86	4.124%	$15.4728	$15.47	$15.45	$15.50
Purchase #5	$53.40	8.610%	$57.9977	$58.00	$58.00	$58.00
Purchase #6	$196.77	4.413%	$205.4535	$205.45	$205.45	$205.50
Purchase #7	$80.94	9.618%	$88.7248	$88.72	$88.70	$88.70
7 purchase totals =	$807.78		$858.9421	$858.93	$858.90	$858.90