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	$27.57	9.822%	$30.2779	$30.28	$30.30	$30.30
Purchase #2	$60.98	10.390%	$67.3158	$67.32	$67.30	$67.30
Purchase #3	$128.55	9.309%	$140.5167	$140.52	$140.50	$140.50
Purchase #4	$209.81	8.485%	$227.6124	$227.61	$227.60	$227.60
Purchase #5	$129.46	12.649%	$145.8354	$145.84	$145.85	$145.80
Purchase #6	$246.43	8.141%	$266.4919	$266.49	$266.50	$266.50
Purchase #7	$212.94	4.455%	$222.4265	$222.43	$222.45	$222.40
7 purchase totals =	$1,015.74		$1,100.4766	$1,100.49	$1,100.50	$1,100.40