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	$9.97	3.672%	$10.3361	$10.34	$10.35	$10.30
Purchase #2	$130.96	11.681%	$146.2574	$146.26	$146.25	$146.30
Purchase #3	$135.46	10.147%	$149.2051	$149.21	$149.20	$149.20
Purchase #4	$105.61	5.421%	$111.3351	$111.34	$111.35	$111.30
Purchase #5	$46.88	6.287%	$49.8273	$49.83	$49.85	$49.80
Purchase #6	$15.38	10.218%	$16.9515	$16.95	$16.95	$17.00
Purchase #7	$43.33	11.119%	$48.1479	$48.15	$48.15	$48.10
7 purchase totals =	$487.59		$532.0604	$532.08	$532.10	$532.00