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	$163.42	6.127%	$173.4327	$173.43	$173.45	$173.40
Purchase #2	$225.57	12.382%	$253.5001	$253.50	$253.50	$253.50
Purchase #3	$10.92	13.421%	$12.3856	$12.39	$12.40	$12.40
Purchase #4	$28.36	10.176%	$31.2459	$31.25	$31.25	$31.20
Purchase #5	$115.70	6.528%	$123.2529	$123.25	$123.25	$123.30
Purchase #6	$150.63	6.603%	$160.5761	$160.58	$160.60	$160.60
Purchase #7	$148.83	6.667%	$158.7525	$158.75	$158.75	$158.80
7 purchase totals =	$843.43		$913.1458	$913.15	$913.20	$913.20