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	$155.47	11.597%	$173.4999	$173.50	$173.50	$173.50
Purchase #2	$228.98	13.834%	$260.6571	$260.66	$260.65	$260.70
Purchase #3	$105.99	5.280%	$111.5863	$111.59	$111.60	$111.60
Purchase #4	$215.83	4.590%	$225.7366	$225.74	$225.75	$225.70
Purchase #5	$126.71	12.340%	$142.346	$142.35	$142.35	$142.30
Purchase #6	$48.34	10.188%	$53.2649	$53.26	$53.25	$53.30
Purchase #7	$28.52	12.153%	$31.986	$31.99	$32.00	$32.00
7 purchase totals =	$909.84		$999.0768	$999.09	$999.10	$999.10