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	$151.59	9.132%	$165.4332	$165.43	$165.45	$165.40
Purchase #2	$131.25	10.831%	$145.4657	$145.47	$145.45	$145.50
Purchase #3	$94.48	5.655%	$99.8228	$99.82	$99.80	$99.80
Purchase #4	$47.99	4.256%	$50.0325	$50.03	$50.05	$50.00
Purchase #5	$246.52	3.838%	$255.9814	$255.98	$256.00	$256.00
Purchase #6	$133.43	13.852%	$151.9127	$151.91	$151.90	$151.90
Purchase #7	$116.78	10.111%	$128.5876	$128.59	$128.60	$128.60
7 purchase totals =	$922.04		$997.2359	$997.23	$997.25	$997.20