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	$136.41	5.204%	$143.5088	$143.51	$143.50	$143.50
Purchase #2	$138.83	11.296%	$154.5122	$154.51	$154.50	$154.50
Purchase #3	$215.74	12.666%	$243.0656	$243.07	$243.05	$243.10
Purchase #4	$155.52	9.725%	$170.6443	$170.64	$170.65	$170.60
Purchase #5	$58.98	10.429%	$65.131	$65.13	$65.15	$65.10
Purchase #6	$85.47	12.497%	$96.1512	$96.15	$96.15	$96.20
Purchase #7	$128.54	13.748%	$146.2117	$146.21	$146.20	$146.20
7 purchase totals =	$919.49		$1,019.2248	$1,019.22	$1,019.20	$1,019.20