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	$56.57	7.342%	$60.7234	$60.72	$60.70	$60.70
Purchase #2	$98.90	12.776%	$111.5355	$111.54	$111.55	$111.50
Purchase #3	$68.77	13.559%	$78.0945	$78.09	$78.10	$78.10
Purchase #4	$86.32	8.215%	$93.4112	$93.41	$93.40	$93.40
Purchase #5	$109.32	6.129%	$116.0202	$116.02	$116.00	$116.00
Purchase #6	$223.49	10.716%	$247.4392	$247.44	$247.45	$247.40
Purchase #7	$205.26	8.103%	$221.8922	$221.89	$221.90	$221.90
7 purchase totals =	$848.63		$929.1162	$929.11	$929.10	$929.00