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	$74.52	4.372%	$77.778	$77.78	$77.80	$77.80
Purchase #2	$40.59	12.149%	$45.5213	$45.52	$45.50	$45.50
Purchase #3	$229.41	11.374%	$255.5031	$255.50	$255.50	$255.50
Purchase #4	$85.85	7.771%	$92.5214	$92.52	$92.50	$92.50
Purchase #5	$34.71	3.477%	$35.9169	$35.92	$35.90	$35.90
Purchase #6	$144.49	11.841%	$161.5991	$161.60	$161.60	$161.60
Purchase #7	$134.65	6.697%	$143.6675	$143.67	$143.65	$143.70
7 purchase totals =	$744.22		$812.5073	$812.51	$812.45	$812.50