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	$40.72	5.189%	$42.833	$42.83	$42.85	$42.80
Purchase #2	$205.38	11.225%	$228.4339	$228.43	$228.45	$228.40
Purchase #3	$245.94	4.365%	$256.6753	$256.68	$256.70	$256.70
Purchase #4	$214.51	9.506%	$234.9013	$234.90	$234.90	$234.90
Purchase #5	$121.31	9.709%	$133.088	$133.09	$133.10	$133.10
Purchase #6	$24.32	4.777%	$25.4818	$25.48	$25.50	$25.50
Purchase #7	$18.74	10.231%	$20.6573	$20.66	$20.65	$20.70
7 purchase totals =	$870.92		$942.0706	$942.07	$942.15	$942.10