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	$32.80	3.766%	$34.0352	$34.04	$34.05	$34.00
Purchase #2	$60.45	13.471%	$68.5932	$68.59	$68.60	$68.60
Purchase #3	$98.90	7.660%	$106.4757	$106.48	$106.50	$106.50
Purchase #4	$74.61	10.103%	$82.1478	$82.15	$82.15	$82.10
Purchase #5	$139.38	5.392%	$146.8954	$146.90	$146.90	$146.90
Purchase #6	$65.78	13.367%	$74.5728	$74.57	$74.55	$74.60
Purchase #7	$43.57	6.753%	$46.5123	$46.51	$46.50	$46.50
7 purchase totals =	$515.49		$559.2324	$559.24	$559.25	$559.20