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	$15.83	12.679%	$17.8371	$17.84	$17.85	$17.80
Purchase #2	$167.59	3.745%	$173.8662	$173.87	$173.85	$173.90
Purchase #3	$118.33	7.725%	$127.471	$127.47	$127.45	$127.50
Purchase #4	$31.41	8.525%	$34.0877	$34.09	$34.10	$34.10
Purchase #5	$71.89	8.650%	$78.1085	$78.11	$78.10	$78.10
Purchase #6	$144.50	4.338%	$150.7684	$150.77	$150.75	$150.80
Purchase #7	$146.52	8.377%	$158.794	$158.79	$158.80	$158.80
7 purchase totals =	$696.07		$740.9329	$740.94	$740.90	$741.00