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	$214.55	11.210%	$238.6011	$238.60	$238.60	$238.60
Purchase #2	$127.33	11.657%	$142.1729	$142.17	$142.15	$142.20
Purchase #3	$108.78	3.324%	$112.3958	$112.40	$112.40	$112.40
Purchase #4	$36.31	12.401%	$40.8128	$40.81	$40.80	$40.80
Purchase #5	$158.48	12.609%	$178.4627	$178.46	$178.45	$178.50
Purchase #6	$48.55	12.607%	$54.6707	$54.67	$54.65	$54.70
Purchase #7	$49.66	11.309%	$55.276	$55.28	$55.30	$55.30
7 purchase totals =	$743.66		$822.3920	$822.39	$822.35	$822.50