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	$7.57	6.708%	$8.0778	$8.08	$8.10	$8.10
Purchase #2	$239.73	10.324%	$264.4797	$264.48	$264.50	$264.50
Purchase #3	$151.78	12.843%	$171.2731	$171.27	$171.25	$171.30
Purchase #4	$220.75	8.347%	$239.176	$239.18	$239.20	$239.20
Purchase #5	$29.89	5.664%	$31.583	$31.58	$31.60	$31.60
Purchase #6	$63.38	12.777%	$71.4781	$71.48	$71.50	$71.50
Purchase #7	$105.95	5.259%	$111.5219	$111.52	$111.50	$111.50
7 purchase totals =	$819.05		$897.5896	$897.59	$897.65	$897.70