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	$23.79	4.520%	$24.8653	$24.87	$24.85	$24.90
Purchase #2	$227.58	9.443%	$249.0704	$249.07	$249.05	$249.10
Purchase #3	$85.90	10.412%	$94.8439	$94.84	$94.85	$94.80
Purchase #4	$189.34	12.269%	$212.5701	$212.57	$212.55	$212.60
Purchase #5	$111.69	5.278%	$117.585	$117.59	$117.60	$117.60
Purchase #6	$166.51	13.837%	$189.55	$189.55	$189.55	$189.60
Purchase #7	$220.47	13.796%	$250.886	$250.89	$250.90	$250.90
7 purchase totals =	$1,025.28		$1,139.3707	$1,139.38	$1,139.35	$1,139.50