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	$21.98	11.430%	$24.4923	$24.49	$24.50	$24.50
Purchase #2	$20.83	11.723%	$23.2719	$23.27	$23.25	$23.30
Purchase #3	$80.92	5.725%	$85.5527	$85.55	$85.55	$85.60
Purchase #4	$192.54	3.412%	$199.1095	$199.11	$199.10	$199.10
Purchase #5	$95.92	10.697%	$106.1806	$106.18	$106.20	$106.20
Purchase #6	$101.66	9.819%	$111.642	$111.64	$111.65	$111.60
Purchase #7	$87.34	10.344%	$96.3744	$96.37	$96.35	$96.40
7 purchase totals =	$601.19		$646.6234	$646.61	$646.60	$646.70