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	$191.67	13.314%	$217.1889	$217.19	$217.20	$217.20
Purchase #2	$50.26	8.274%	$54.4185	$54.42	$54.40	$54.40
Purchase #3	$143.67	3.624%	$148.8766	$148.88	$148.90	$148.90
Purchase #4	$29.47	10.556%	$32.5809	$32.58	$32.60	$32.60
Purchase #5	$65.88	6.598%	$70.2268	$70.23	$70.25	$70.20
Purchase #6	$117.75	11.707%	$131.535	$131.54	$131.55	$131.50
Purchase #7	$157.61	3.325%	$162.8505	$162.85	$162.85	$162.90
7 purchase totals =	$756.31		$817.6772	$817.69	$817.75	$817.70