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	$55.74	3.292%	$57.575	$57.58	$57.60	$57.60
Purchase #2	$229.92	9.791%	$252.4315	$252.43	$252.45	$252.40
Purchase #3	$231.91	4.278%	$241.8311	$241.83	$241.85	$241.80
Purchase #4	$132.64	4.411%	$138.4908	$138.49	$138.50	$138.50
Purchase #5	$200.69	6.664%	$214.064	$214.06	$214.05	$214.10
Purchase #6	$43.88	13.552%	$49.8266	$49.83	$49.85	$49.80
Purchase #7	$139.86	4.726%	$146.4698	$146.47	$146.45	$146.50
7 purchase totals =	$1,034.64		$1,100.6888	$1,100.69	$1,100.75	$1,100.70