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	$101.88	6.476%	$108.4777	$108.48	$108.50	$108.50
Purchase #2	$221.90	11.678%	$247.8135	$247.81	$247.80	$247.80
Purchase #3	$37.66	11.738%	$42.0805	$42.08	$42.10	$42.10
Purchase #4	$40.76	12.342%	$45.7906	$45.79	$45.80	$45.80
Purchase #5	$31.46	10.418%	$34.7375	$34.74	$34.75	$34.70
Purchase #6	$11.54	12.622%	$12.9966	$13.00	$13.00	$13.00
Purchase #7	$127.92	12.251%	$143.5915	$143.59	$143.60	$143.60
7 purchase totals =	$573.12		$635.4879	$635.49	$635.55	$635.50