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	$160.69	3.857%	$166.8878	$166.89	$166.90	$166.90
Purchase #2	$59.68	3.624%	$61.8428	$61.84	$61.85	$61.80
Purchase #3	$214.47	6.388%	$228.1703	$228.17	$228.15	$228.20
Purchase #4	$87.93	8.602%	$95.4937	$95.49	$95.50	$95.50
Purchase #5	$199.25	12.183%	$223.5246	$223.52	$223.50	$223.50
Purchase #6	$56.53	8.792%	$61.5001	$61.50	$61.50	$61.50
Purchase #7	$32.79	11.191%	$36.4595	$36.46	$36.45	$36.50
7 purchase totals =	$811.34		$873.8788	$873.87	$873.85	$873.90