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	$218.45	9.222%	$238.5955	$238.60	$238.60	$238.60
Purchase #2	$15.31	10.103%	$16.8568	$16.86	$16.85	$16.90
Purchase #3	$183.56	9.213%	$200.4714	$200.47	$200.45	$200.50
Purchase #4	$91.93	9.729%	$100.8739	$100.87	$100.85	$100.90
Purchase #5	$11.68	9.395%	$12.7773	$12.78	$12.80	$12.80
Purchase #6	$48.61	8.129%	$52.5615	$52.56	$52.55	$52.60
Purchase #7	$36.91	3.685%	$38.2701	$38.27	$38.25	$38.30
7 purchase totals =	$606.45		$660.4065	$660.41	$660.35	$660.60