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	$90.36	8.188%	$97.7587	$97.76	$97.75	$97.80
Purchase #2	$87.75	3.154%	$90.5176	$90.52	$90.50	$90.50
Purchase #3	$41.27	13.428%	$46.8117	$46.81	$46.80	$46.80
Purchase #4	$50.71	9.385%	$55.4691	$55.47	$55.45	$55.50
Purchase #5	$124.85	11.492%	$139.1978	$139.20	$139.20	$139.20
Purchase #6	$125.95	6.137%	$133.6796	$133.68	$133.70	$133.70
Purchase #7	$235.72	11.340%	$262.4506	$262.45	$262.45	$262.50
7 purchase totals =	$756.61		$825.8851	$825.89	$825.85	$826.00