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	$103.70	9.104%	$113.1408	$113.14	$113.15	$113.10
Purchase #2	$35.42	11.553%	$39.5121	$39.51	$39.50	$39.50
Purchase #3	$35.99	12.325%	$40.4258	$40.43	$40.45	$40.40
Purchase #4	$45.52	12.196%	$51.0716	$51.07	$51.05	$51.10
Purchase #5	$196.41	13.764%	$223.4439	$223.44	$223.45	$223.40
Purchase #6	$90.25	3.350%	$93.2734	$93.27	$93.25	$93.30
Purchase #7	$222.36	8.791%	$241.9077	$241.91	$241.90	$241.90
7 purchase totals =	$729.65		$802.7753	$802.77	$802.75	$802.70