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	$217.61	6.551%	$231.8656	$231.87	$231.85	$231.90
Purchase #2	$183.38	11.869%	$205.1454	$205.15	$205.15	$205.10
Purchase #3	$126.38	4.684%	$132.2996	$132.30	$132.30	$132.30
Purchase #4	$12.80	5.628%	$13.5204	$13.52	$13.50	$13.50
Purchase #5	$136.55	11.252%	$151.9146	$151.91	$151.90	$151.90
Purchase #6	$143.81	12.823%	$162.2508	$162.25	$162.25	$162.30
Purchase #7	$40.46	3.814%	$42.0031	$42.00	$42.00	$42.00
7 purchase totals =	$860.99		$938.9995	$939.00	$938.95	$939.00