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	$99.37	13.136%	$112.4232	$112.42	$112.40	$112.40
Purchase #2	$114.42	10.255%	$126.1538	$126.15	$126.15	$126.20
Purchase #3	$204.56	12.285%	$229.6902	$229.69	$229.70	$229.70
Purchase #4	$61.53	5.835%	$65.1203	$65.12	$65.10	$65.10
Purchase #5	$18.82	4.198%	$19.6101	$19.61	$19.60	$19.60
Purchase #6	$123.53	6.271%	$131.2766	$131.28	$131.30	$131.30
Purchase #7	$119.82	10.336%	$132.2046	$132.20	$132.20	$132.20
7 purchase totals =	$742.05		$816.4788	$816.47	$816.45	$816.50