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	$123.65	13.434%	$140.2611	$140.26	$140.25	$140.30
Purchase #2	$57.86	6.189%	$61.441	$61.44	$61.45	$61.40
Purchase #3	$123.38	3.414%	$127.5922	$127.59	$127.60	$127.60
Purchase #4	$67.31	6.103%	$71.4179	$71.42	$71.40	$71.40
Purchase #5	$92.26	12.127%	$103.4484	$103.45	$103.45	$103.40
Purchase #6	$48.72	12.615%	$54.866	$54.87	$54.85	$54.90
Purchase #7	$69.90	4.430%	$72.9966	$73.00	$73.00	$73.00
7 purchase totals =	$583.08		$632.0232	$632.03	$632.00	$632.00