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	$211.44	12.491%	$237.851	$237.85	$237.85	$237.90
Purchase #2	$103.78	11.867%	$116.0956	$116.10	$116.10	$116.10
Purchase #3	$39.58	3.538%	$40.9803	$40.98	$41.00	$41.00
Purchase #4	$160.82	7.500%	$172.8815	$172.88	$172.90	$172.90
Purchase #5	$155.44	6.466%	$165.4908	$165.49	$165.50	$165.50
Purchase #6	$31.79	10.103%	$35.0017	$35.00	$35.00	$35.00
Purchase #7	$179.27	6.314%	$190.5891	$190.59	$190.60	$190.60
7 purchase totals =	$882.12		$958.8900	$958.89	$958.95	$959.00