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	$71.46	4.847%	$74.9237	$74.92	$74.90	$74.90
Purchase #2	$112.77	11.386%	$125.61	$125.61	$125.60	$125.60
Purchase #3	$41.65	8.497%	$45.189	$45.19	$45.20	$45.20
Purchase #4	$96.89	11.813%	$108.3356	$108.34	$108.35	$108.30
Purchase #5	$104.47	6.705%	$111.4747	$111.47	$111.45	$111.50
Purchase #6	$18.62	13.189%	$21.0758	$21.08	$21.10	$21.10
Purchase #7	$22.75	8.110%	$24.595	$24.60	$24.60	$24.60
7 purchase totals =	$468.61		$511.2038	$511.21	$511.20	$511.20