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	$75.41	4.216%	$78.5893	$78.59	$78.60	$78.60
Purchase #2	$139.52	4.692%	$146.0663	$146.07	$146.05	$146.10
Purchase #3	$87.83	5.403%	$92.5755	$92.58	$92.60	$92.60
Purchase #4	$151.52	9.318%	$165.6386	$165.64	$165.65	$165.60
Purchase #5	$106.30	6.296%	$112.9926	$112.99	$113.00	$113.00
Purchase #6	$173.33	10.110%	$190.8537	$190.85	$190.85	$190.90
Purchase #7	$14.84	13.221%	$16.802	$16.80	$16.80	$16.80
7 purchase totals =	$748.75		$803.5180	$803.52	$803.55	$803.60