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	$61.39	4.276%	$64.015	$64.02	$64.00	$64.00
Purchase #2	$116.34	6.147%	$123.4914	$123.49	$123.50	$123.50
Purchase #3	$95.90	4.866%	$100.5665	$100.57	$100.55	$100.60
Purchase #4	$9.30	6.301%	$9.886	$9.89	$9.90	$9.90
Purchase #5	$99.49	6.216%	$105.6743	$105.67	$105.65	$105.70
Purchase #6	$125.41	10.105%	$138.0827	$138.08	$138.10	$138.10
Purchase #7	$36.88	8.581%	$40.0447	$40.04	$40.05	$40.00
7 purchase totals =	$544.71		$581.7606	$581.76	$581.75	$581.80