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	$167.87	13.472%	$190.4854	$190.49	$190.50	$190.50
Purchase #2	$116.69	6.162%	$123.8804	$123.88	$123.90	$123.90
Purchase #3	$238.97	11.425%	$266.2723	$266.27	$266.25	$266.30
Purchase #4	$163.87	5.255%	$172.4814	$172.48	$172.50	$172.50
Purchase #5	$104.67	6.283%	$111.2464	$111.25	$111.25	$111.20
Purchase #6	$36.26	5.249%	$38.1633	$38.16	$38.15	$38.20
Purchase #7	$20.90	11.463%	$23.2958	$23.30	$23.30	$23.30
7 purchase totals =	$849.23		$925.8250	$925.83	$925.85	$925.90