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	$166.53	13.776%	$189.4712	$189.47	$189.45	$189.50
Purchase #2	$30.81	5.863%	$32.6164	$32.62	$32.60	$32.60
Purchase #3	$172.29	9.422%	$188.5232	$188.52	$188.50	$188.50
Purchase #4	$167.96	9.179%	$183.377	$183.38	$183.40	$183.40
Purchase #5	$25.89	5.518%	$27.3186	$27.32	$27.30	$27.30
Purchase #6	$249.57	8.620%	$271.0829	$271.08	$271.10	$271.10
Purchase #7	$16.78	9.788%	$18.4224	$18.42	$18.40	$18.40
7 purchase totals =	$829.83		$910.8117	$910.81	$910.75	$910.80