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	$192.92	12.828%	$217.6678	$217.67	$217.65	$217.70
Purchase #2	$98.40	6.205%	$104.5057	$104.51	$104.50	$104.50
Purchase #3	$38.92	5.509%	$41.0641	$41.06	$41.05	$41.10
Purchase #4	$65.92	9.754%	$72.3498	$72.35	$72.35	$72.30
Purchase #5	$153.42	12.835%	$173.1115	$173.11	$173.10	$173.10
Purchase #6	$66.86	5.345%	$70.4337	$70.43	$70.45	$70.40
Purchase #7	$29.53	9.335%	$32.2866	$32.29	$32.30	$32.30
7 purchase totals =	$645.97		$711.4192	$711.42	$711.40	$711.40