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	$16.48	11.752%	$18.4167	$18.42	$18.40	$18.40
Purchase #2	$42.86	8.673%	$46.5772	$46.58	$46.60	$46.60
Purchase #3	$225.87	8.825%	$245.803	$245.80	$245.80	$245.80
Purchase #4	$129.95	5.747%	$137.4182	$137.42	$137.40	$137.40
Purchase #5	$38.52	10.145%	$42.4279	$42.43	$42.45	$42.40
Purchase #6	$231.46	13.210%	$262.0359	$262.04	$262.05	$262.00
Purchase #7	$101.42	4.478%	$105.9616	$105.96	$105.95	$106.00
7 purchase totals =	$786.56		$858.6405	$858.65	$858.65	$858.60