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	$12.32	11.854%	$13.7804	$13.78	$13.80	$13.80
Purchase #2	$130.35	10.396%	$143.9012	$143.90	$143.90	$143.90
Purchase #3	$73.72	3.308%	$76.1587	$76.16	$76.15	$76.20
Purchase #4	$155.25	10.864%	$172.1164	$172.12	$172.10	$172.10
Purchase #5	$182.50	12.137%	$204.65	$204.65	$204.65	$204.70
Purchase #6	$33.77	5.146%	$35.5078	$35.51	$35.50	$35.50
Purchase #7	$132.49	13.507%	$150.3854	$150.39	$150.40	$150.40
7 purchase totals =	$720.40		$796.4999	$796.51	$796.50	$796.60