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	$105.36	12.431%	$118.4573	$118.46	$118.45	$118.50
Purchase #2	$102.59	5.574%	$108.3084	$108.31	$108.30	$108.30
Purchase #3	$61.36	12.653%	$69.1239	$69.12	$69.10	$69.10
Purchase #4	$105.83	5.214%	$111.348	$111.35	$111.35	$111.30
Purchase #5	$197.89	3.845%	$205.4989	$205.50	$205.50	$205.50
Purchase #6	$33.62	6.800%	$35.9062	$35.91	$35.90	$35.90
Purchase #7	$30.98	12.357%	$34.8082	$34.81	$34.80	$34.80
7 purchase totals =	$637.63		$683.4509	$683.46	$683.40	$683.40