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	$96.85	4.160%	$100.879	$100.88	$100.90	$100.90
Purchase #2	$131.46	9.607%	$144.0894	$144.09	$144.10	$144.10
Purchase #3	$128.40	11.697%	$143.4189	$143.42	$143.40	$143.40
Purchase #4	$121.25	4.325%	$126.4941	$126.49	$126.50	$126.50
Purchase #5	$203.28	3.107%	$209.5959	$209.60	$209.60	$209.60
Purchase #6	$83.26	8.167%	$90.0598	$90.06	$90.05	$90.10
Purchase #7	$30.88	11.624%	$34.4695	$34.47	$34.45	$34.50
7 purchase totals =	$795.38		$849.0066	$849.01	$849.00	$849.10