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	$246.96	10.652%	$273.2662	$273.27	$273.25	$273.30
Purchase #2	$66.68	7.790%	$71.8744	$71.87	$71.85	$71.90
Purchase #3	$154.52	13.627%	$175.5764	$175.58	$175.60	$175.60
Purchase #4	$76.55	11.108%	$85.0532	$85.05	$85.05	$85.10
Purchase #5	$139.71	4.344%	$145.779	$145.78	$145.80	$145.80
Purchase #6	$77.67	5.465%	$81.9147	$81.91	$81.90	$81.90
Purchase #7	$103.83	10.128%	$114.3459	$114.35	$114.35	$114.30
7 purchase totals =	$865.92		$947.8098	$947.81	$947.80	$947.90