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	$112.53	13.498%	$127.7193	$127.72	$127.70	$127.70
Purchase #2	$93.82	12.689%	$105.7248	$105.72	$105.70	$105.70
Purchase #3	$137.86	4.504%	$144.0692	$144.07	$144.05	$144.10
Purchase #4	$63.46	11.328%	$70.6487	$70.65	$70.65	$70.60
Purchase #5	$245.42	10.267%	$270.6173	$270.62	$270.60	$270.60
Purchase #6	$14.34	6.198%	$15.2288	$15.23	$15.25	$15.20
Purchase #7	$123.26	13.328%	$139.6881	$139.69	$139.70	$139.70
7 purchase totals =	$790.69		$873.6962	$873.70	$873.65	$873.60