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	$9.85	9.861%	$10.8213	$10.82	$10.80	$10.80
Purchase #2	$100.93	3.118%	$104.077	$104.08	$104.10	$104.10
Purchase #3	$127.32	11.615%	$142.1082	$142.11	$142.10	$142.10
Purchase #4	$10.71	11.754%	$11.9689	$11.97	$11.95	$12.00
Purchase #5	$113.48	12.118%	$127.2315	$127.23	$127.25	$127.20
Purchase #6	$227.98	13.692%	$259.195	$259.20	$259.20	$259.20
Purchase #7	$187.95	6.794%	$200.7193	$200.72	$200.70	$200.70
7 purchase totals =	$778.22		$856.1212	$856.13	$856.10	$856.10