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	$95.59	3.815%	$99.2368	$99.24	$99.25	$99.20
Purchase #2	$112.64	13.683%	$128.0525	$128.05	$128.05	$128.10
Purchase #3	$198.66	13.549%	$225.5764	$225.58	$225.60	$225.60
Purchase #4	$225.51	13.747%	$256.5109	$256.51	$256.50	$256.50
Purchase #5	$9.65	10.246%	$10.6387	$10.64	$10.65	$10.60
Purchase #6	$60.81	11.596%	$67.8615	$67.86	$67.85	$67.90
Purchase #7	$160.54	11.487%	$178.9812	$178.98	$179.00	$179.00
7 purchase totals =	$863.40		$966.8580	$966.86	$966.90	$966.90