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	$20.64	3.383%	$21.3383	$21.34	$21.35	$21.30
Purchase #2	$128.70	11.819%	$143.9111	$143.91	$143.90	$143.90
Purchase #3	$69.74	4.580%	$72.9341	$72.93	$72.95	$72.90
Purchase #4	$27.85	8.788%	$30.2975	$30.30	$30.30	$30.30
Purchase #5	$40.46	3.436%	$41.8502	$41.85	$41.85	$41.90
Purchase #6	$245.69	12.182%	$275.62	$275.62	$275.60	$275.60
Purchase #7	$214.52	4.456%	$224.079	$224.08	$224.10	$224.10
7 purchase totals =	$747.60		$810.0302	$810.03	$810.05	$810.00