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	$37.72	13.657%	$42.8714	$42.87	$42.85	$42.90
Purchase #2	$243.93	8.209%	$263.9542	$263.95	$263.95	$264.00
Purchase #3	$95.38	3.828%	$99.0311	$99.03	$99.05	$99.00
Purchase #4	$234.90	3.268%	$242.5765	$242.58	$242.60	$242.60
Purchase #5	$77.60	4.735%	$81.2744	$81.27	$81.25	$81.30
Purchase #6	$91.80	8.398%	$99.5094	$99.51	$99.50	$99.50
Purchase #7	$16.79	6.290%	$17.8461	$17.85	$17.85	$17.80
7 purchase totals =	$798.12		$847.0631	$847.06	$847.05	$847.10