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	$63.42	9.460%	$69.4195	$69.42	$69.40	$69.40
Purchase #2	$112.54	13.392%	$127.6114	$127.61	$127.60	$127.60
Purchase #3	$228.81	13.127%	$258.8459	$258.85	$258.85	$258.80
Purchase #4	$248.65	12.578%	$279.9252	$279.93	$279.95	$279.90
Purchase #5	$29.61	12.766%	$33.39	$33.39	$33.40	$33.40
Purchase #6	$122.97	13.522%	$139.598	$139.60	$139.60	$139.60
Purchase #7	$37.66	5.176%	$39.6093	$39.61	$39.60	$39.60
7 purchase totals =	$843.66		$948.3993	$948.41	$948.40	$948.30