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	$63.90	7.139%	$68.4618	$68.46	$68.45	$68.50
Purchase #2	$36.46	11.219%	$40.5504	$40.55	$40.55	$40.60
Purchase #3	$189.52	3.708%	$196.5474	$196.55	$196.55	$196.50
Purchase #4	$205.43	13.345%	$232.8446	$232.84	$232.85	$232.80
Purchase #5	$54.99	9.792%	$60.3746	$60.37	$60.35	$60.40
Purchase #6	$204.71	11.145%	$227.5249	$227.52	$227.50	$227.50
Purchase #7	$132.28	8.488%	$143.5079	$143.51	$143.50	$143.50
7 purchase totals =	$887.29		$969.8116	$969.80	$969.75	$969.80