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	$38.47	8.702%	$41.8177	$41.82	$41.80	$41.80
Purchase #2	$107.63	3.230%	$111.1064	$111.11	$111.10	$111.10
Purchase #3	$75.51	4.240%	$78.7116	$78.71	$78.70	$78.70
Purchase #4	$19.29	6.268%	$20.4991	$20.50	$20.50	$20.50
Purchase #5	$238.78	6.778%	$254.9645	$254.96	$254.95	$255.00
Purchase #6	$68.56	11.444%	$76.406	$76.41	$76.40	$76.40
Purchase #7	$41.60	7.427%	$44.6896	$44.69	$44.70	$44.70
7 purchase totals =	$589.84		$628.1949	$628.20	$628.15	$628.20