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	$223.46	3.103%	$230.394	$230.39	$230.40	$230.40
Purchase #2	$85.51	4.401%	$89.2733	$89.27	$89.25	$89.30
Purchase #3	$30.55	8.335%	$33.0963	$33.10	$33.10	$33.10
Purchase #4	$31.81	11.605%	$35.5016	$35.50	$35.50	$35.50
Purchase #5	$6.46	6.721%	$6.8942	$6.89	$6.90	$6.90
Purchase #6	$88.27	12.390%	$99.2067	$99.21	$99.20	$99.20
Purchase #7	$35.65	6.698%	$38.0378	$38.04	$38.05	$38.00
7 purchase totals =	$501.71		$532.4039	$532.40	$532.40	$532.40