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	$18.47	8.769%	$20.0896	$20.09	$20.10	$20.10
Purchase #2	$77.56	7.799%	$83.6089	$83.61	$83.60	$83.60
Purchase #3	$127.51	11.133%	$141.7057	$141.71	$141.70	$141.70
Purchase #4	$62.40	6.146%	$66.2351	$66.24	$66.25	$66.20
Purchase #5	$7.42	10.821%	$8.2229	$8.22	$8.20	$8.20
Purchase #6	$74.98	10.547%	$82.8881	$82.89	$82.90	$82.90
Purchase #7	$244.66	12.345%	$274.8633	$274.86	$274.85	$274.90
7 purchase totals =	$613.00		$677.6136	$677.62	$677.60	$677.60