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	$154.92	10.294%	$170.8675	$170.87	$170.85	$170.90
Purchase #2	$187.43	9.295%	$204.8516	$204.85	$204.85	$204.90
Purchase #3	$222.52	13.257%	$252.0195	$252.02	$252.00	$252.00
Purchase #4	$173.52	9.739%	$190.4191	$190.42	$190.40	$190.40
Purchase #5	$100.64	4.807%	$105.4778	$105.48	$105.50	$105.50
Purchase #6	$62.38	12.819%	$70.3765	$70.38	$70.40	$70.40
Purchase #7	$9.37	9.762%	$10.2847	$10.28	$10.30	$10.30
7 purchase totals =	$910.78		$1,004.2967	$1,004.30	$1,004.30	$1,004.40