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	$60.71	8.162%	$65.6652	$65.67	$65.65	$65.70
Purchase #2	$40.45	12.549%	$45.5261	$45.53	$45.55	$45.50
Purchase #3	$225.36	7.759%	$242.8457	$242.85	$242.85	$242.80
Purchase #4	$98.34	6.252%	$104.4882	$104.49	$104.50	$104.50
Purchase #5	$151.79	5.797%	$160.5893	$160.59	$160.60	$160.60
Purchase #6	$26.83	10.465%	$29.6378	$29.64	$29.65	$29.60
Purchase #7	$63.88	3.619%	$66.1918	$66.19	$66.20	$66.20
7 purchase totals =	$667.36		$714.9441	$714.96	$715.00	$714.90