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	$38.34	9.700%	$42.059	$42.06	$42.05	$42.10
Purchase #2	$10.29	9.403%	$11.2576	$11.26	$11.25	$11.30
Purchase #3	$14.89	6.601%	$15.8729	$15.87	$15.85	$15.90
Purchase #4	$118.35	8.641%	$128.5766	$128.58	$128.60	$128.60
Purchase #5	$89.85	6.683%	$95.8547	$95.85	$95.85	$95.90
Purchase #6	$111.64	8.555%	$121.1908	$121.19	$121.20	$121.20
Purchase #7	$168.41	13.712%	$191.5024	$191.50	$191.50	$191.50
7 purchase totals =	$551.77		$606.3140	$606.31	$606.30	$606.50