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	$240.75	6.279%	$255.8667	$255.87	$255.85	$255.90
Purchase #2	$10.30	3.772%	$10.6885	$10.69	$10.70	$10.70
Purchase #3	$54.97	10.788%	$60.9002	$60.90	$60.90	$60.90
Purchase #4	$37.64	7.152%	$40.332	$40.33	$40.35	$40.30
Purchase #5	$161.35	6.566%	$171.9442	$171.94	$171.95	$171.90
Purchase #6	$242.41	5.560%	$255.888	$255.89	$255.90	$255.90
Purchase #7	$15.42	8.291%	$16.6985	$16.70	$16.70	$16.70
7 purchase totals =	$762.84		$812.3181	$812.32	$812.35	$812.30