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	$240.89	6.651%	$256.9116	$256.91	$256.90	$256.90
Purchase #2	$184.94	5.284%	$194.7122	$194.71	$194.70	$194.70
Purchase #3	$221.51	7.412%	$237.9283	$237.93	$237.95	$237.90
Purchase #4	$174.37	7.741%	$187.868	$187.87	$187.85	$187.90
Purchase #5	$51.45	10.491%	$56.8476	$56.85	$56.85	$56.80
Purchase #6	$87.83	8.843%	$95.5968	$95.60	$95.60	$95.60
Purchase #7	$57.86	13.537%	$65.6925	$65.69	$65.70	$65.70
7 purchase totals =	$1,018.85		$1,095.5570	$1,095.56	$1,095.55	$1,095.50