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	$236.61	12.639%	$266.5151	$266.52	$266.50	$266.50
Purchase #2	$62.66	6.755%	$66.8927	$66.89	$66.90	$66.90
Purchase #3	$19.67	4.190%	$20.4942	$20.49	$20.50	$20.50
Purchase #4	$12.74	10.177%	$14.0365	$14.04	$14.05	$14.00
Purchase #5	$180.43	10.239%	$198.9042	$198.90	$198.90	$198.90
Purchase #6	$217.91	12.255%	$244.6149	$244.61	$244.60	$244.60
Purchase #7	$32.80	9.337%	$35.8625	$35.86	$35.85	$35.90
7 purchase totals =	$762.82		$847.3201	$847.31	$847.30	$847.30