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	$38.85	7.633%	$41.8154	$41.82	$41.80	$41.80
Purchase #2	$62.78	13.872%	$71.4888	$71.49	$71.50	$71.50
Purchase #3	$135.65	11.722%	$151.5509	$151.55	$151.55	$151.60
Purchase #4	$60.89	12.391%	$68.4349	$68.43	$68.45	$68.40
Purchase #5	$131.26	7.717%	$141.3893	$141.39	$141.40	$141.40
Purchase #6	$220.90	4.606%	$231.0747	$231.07	$231.05	$231.10
Purchase #7	$243.96	11.601%	$272.2618	$272.26	$272.25	$272.30
7 purchase totals =	$894.29		$978.0158	$978.01	$978.00	$978.10