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	$46.89	4.256%	$48.8856	$48.89	$48.90	$48.90
Purchase #2	$143.85	7.718%	$154.9523	$154.95	$154.95	$155.00
Purchase #3	$66.39	11.552%	$74.0594	$74.06	$74.05	$74.10
Purchase #4	$248.94	11.827%	$278.3821	$278.38	$278.40	$278.40
Purchase #5	$35.51	5.570%	$37.4879	$37.49	$37.50	$37.50
Purchase #6	$138.51	10.776%	$153.4358	$153.44	$153.45	$153.40
Purchase #7	$146.56	13.333%	$166.1008	$166.10	$166.10	$166.10
7 purchase totals =	$826.65		$913.3039	$913.31	$913.35	$913.40