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	$64.90	11.382%	$72.2869	$72.29	$72.30	$72.30
Purchase #2	$217.78	6.711%	$232.3952	$232.40	$232.40	$232.40
Purchase #3	$222.82	8.239%	$241.1781	$241.18	$241.20	$241.20
Purchase #4	$56.45	6.230%	$59.9668	$59.97	$59.95	$60.00
Purchase #5	$158.38	9.170%	$172.9034	$172.90	$172.90	$172.90
Purchase #6	$232.59	7.283%	$249.5295	$249.53	$249.55	$249.50
Purchase #7	$42.43	11.204%	$47.1839	$47.18	$47.20	$47.20
7 purchase totals =	$995.35		$1,075.4438	$1,075.45	$1,075.50	$1,075.50