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	$216.85	6.334%	$230.5853	$230.59	$230.60	$230.60
Purchase #2	$152.53	8.296%	$165.1839	$165.18	$165.20	$165.20
Purchase #3	$105.63	11.773%	$118.0658	$118.07	$118.05	$118.10
Purchase #4	$30.90	10.313%	$34.0867	$34.09	$34.10	$34.10
Purchase #5	$142.34	13.304%	$161.2769	$161.28	$161.30	$161.30
Purchase #6	$93.59	11.658%	$104.5007	$104.50	$104.50	$104.50
Purchase #7	$108.75	13.553%	$123.4889	$123.49	$123.50	$123.50
7 purchase totals =	$850.59		$937.1882	$937.20	$937.25	$937.30