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	$184.60	11.462%	$205.7589	$205.76	$205.75	$205.80
Purchase #2	$42.81	6.231%	$45.4775	$45.48	$45.50	$45.50
Purchase #3	$93.52	10.584%	$103.4182	$103.42	$103.40	$103.40
Purchase #4	$82.96	12.509%	$93.3375	$93.34	$93.35	$93.30
Purchase #5	$125.74	8.228%	$136.0859	$136.09	$136.10	$136.10
Purchase #6	$208.55	12.708%	$235.0525	$235.05	$235.05	$235.10
Purchase #7	$88.82	13.551%	$100.856	$100.86	$100.85	$100.90
7 purchase totals =	$827.00		$919.9865	$920.00	$920.00	$920.10