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	$101.39	10.311%	$111.8443	$111.84	$111.85	$111.80
Purchase #2	$107.90	6.403%	$114.8088	$114.81	$114.80	$114.80
Purchase #3	$202.40	13.390%	$229.5014	$229.50	$229.50	$229.50
Purchase #4	$131.80	8.734%	$143.3114	$143.31	$143.30	$143.30
Purchase #5	$112.28	9.427%	$122.8646	$122.86	$122.85	$122.90
Purchase #6	$104.74	6.872%	$111.9377	$111.94	$111.95	$111.90
Purchase #7	$87.58	9.263%	$95.6925	$95.69	$95.70	$95.70
7 purchase totals =	$848.09		$929.9607	$929.95	$929.95	$929.90