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	$106.68	4.595%	$111.5819	$111.58	$111.60	$111.60
Purchase #2	$122.86	5.823%	$130.0141	$130.01	$130.00	$130.00
Purchase #3	$240.98	8.307%	$260.9982	$261.00	$261.00	$261.00
Purchase #4	$85.66	11.849%	$95.8099	$95.81	$95.80	$95.80
Purchase #5	$99.46	12.450%	$111.8428	$111.84	$111.85	$111.80
Purchase #6	$38.73	4.146%	$40.3357	$40.34	$40.35	$40.30
Purchase #7	$74.94	8.665%	$81.4336	$81.43	$81.45	$81.40
7 purchase totals =	$769.31		$832.0162	$832.01	$832.05	$831.90