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	$130.59	3.831%	$135.5929	$135.59	$135.60	$135.60
Purchase #2	$180.95	8.629%	$196.5642	$196.56	$196.55	$196.60
Purchase #3	$34.27	4.169%	$35.6987	$35.70	$35.70	$35.70
Purchase #4	$135.73	3.104%	$139.9431	$139.94	$139.95	$139.90
Purchase #5	$112.94	12.791%	$127.3862	$127.39	$127.40	$127.40
Purchase #6	$66.25	5.678%	$70.0117	$70.01	$70.00	$70.00
Purchase #7	$129.57	12.365%	$145.5913	$145.59	$145.60	$145.60
7 purchase totals =	$790.30		$850.7881	$850.78	$850.80	$850.80