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	$225.64	6.368%	$240.0088	$240.01	$240.00	$240.00
Purchase #2	$126.42	4.330%	$131.894	$131.89	$131.90	$131.90
Purchase #3	$144.80	10.177%	$159.5363	$159.54	$159.55	$159.50
Purchase #4	$9.85	4.549%	$10.2981	$10.30	$10.30	$10.30
Purchase #5	$23.31	6.712%	$24.8746	$24.87	$24.85	$24.90
Purchase #6	$30.89	11.140%	$34.3311	$34.33	$34.35	$34.30
Purchase #7	$78.94	10.367%	$87.1237	$87.12	$87.10	$87.10
7 purchase totals =	$639.85		$688.0666	$688.06	$688.05	$688.00