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	$165.86	11.487%	$184.9123	$184.91	$184.90	$184.90
Purchase #2	$38.69	3.276%	$39.9575	$39.96	$39.95	$40.00
Purchase #3	$183.69	11.872%	$205.4977	$205.50	$205.50	$205.50
Purchase #4	$235.47	8.604%	$255.7298	$255.73	$255.75	$255.70
Purchase #5	$51.71	6.192%	$54.9119	$54.91	$54.90	$54.90
Purchase #6	$80.72	8.854%	$87.8669	$87.87	$87.85	$87.90
Purchase #7	$83.72	4.726%	$87.6766	$87.68	$87.70	$87.70
7 purchase totals =	$839.86		$916.5527	$916.56	$916.55	$916.60