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	$129.86	10.502%	$143.4979	$143.50	$143.50	$143.50
Purchase #2	$108.51	13.658%	$123.3303	$123.33	$123.35	$123.30
Purchase #3	$125.48	12.523%	$141.1939	$141.19	$141.20	$141.20
Purchase #4	$163.43	9.418%	$178.8218	$178.82	$178.80	$178.80
Purchase #5	$137.54	3.627%	$142.5286	$142.53	$142.55	$142.50
Purchase #6	$103.35	7.414%	$111.0124	$111.01	$111.00	$111.00
Purchase #7	$116.89	6.193%	$124.129	$124.13	$124.15	$124.10
7 purchase totals =	$885.06		$964.5139	$964.51	$964.55	$964.40