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	$46.93	12.509%	$52.8005	$52.80	$52.80	$52.80
Purchase #2	$37.75	11.653%	$42.149	$42.15	$42.15	$42.10
Purchase #3	$25.49	6.216%	$27.0745	$27.07	$27.05	$27.10
Purchase #4	$79.44	12.759%	$89.5757	$89.58	$89.60	$89.60
Purchase #5	$172.85	3.323%	$178.5938	$178.59	$178.60	$178.60
Purchase #6	$204.93	8.732%	$222.8245	$222.82	$222.80	$222.80
Purchase #7	$154.69	11.435%	$172.3788	$172.38	$172.40	$172.40
7 purchase totals =	$722.08		$785.3968	$785.39	$785.40	$785.40