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	$233.67	6.746%	$249.4334	$249.43	$249.45	$249.40
Purchase #2	$114.30	11.617%	$127.5782	$127.58	$127.60	$127.60
Purchase #3	$122.72	4.327%	$128.0301	$128.03	$128.05	$128.00
Purchase #4	$138.96	4.318%	$144.9603	$144.96	$144.95	$145.00
Purchase #5	$71.88	13.283%	$81.4278	$81.43	$81.45	$81.40
Purchase #6	$34.31	3.825%	$35.6224	$35.62	$35.60	$35.60
Purchase #7	$33.72	9.333%	$36.8671	$36.87	$36.85	$36.90
7 purchase totals =	$749.56		$803.9193	$803.92	$803.95	$803.90