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	$76.89	4.784%	$80.5684	$80.57	$80.55	$80.60
Purchase #2	$35.86	12.123%	$40.2073	$40.21	$40.20	$40.20
Purchase #3	$176.47	13.628%	$200.5193	$200.52	$200.50	$200.50
Purchase #4	$13.34	3.137%	$13.7585	$13.76	$13.75	$13.80
Purchase #5	$12.30	10.592%	$13.6028	$13.60	$13.60	$13.60
Purchase #6	$195.70	9.572%	$214.4324	$214.43	$214.45	$214.40
Purchase #7	$116.47	6.396%	$123.9194	$123.92	$123.90	$123.90
7 purchase totals =	$627.03		$687.0081	$687.01	$686.95	$687.00