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	$62.40	5.789%	$66.0123	$66.01	$66.00	$66.00
Purchase #2	$234.37	11.215%	$260.6546	$260.65	$260.65	$260.70
Purchase #3	$149.73	10.109%	$164.8662	$164.87	$164.85	$164.90
Purchase #4	$52.54	8.168%	$56.8315	$56.83	$56.85	$56.80
Purchase #5	$117.34	3.531%	$121.4833	$121.48	$121.50	$121.50
Purchase #6	$245.40	4.208%	$255.7264	$255.73	$255.75	$255.70
Purchase #7	$39.99	9.726%	$43.8794	$43.88	$43.90	$43.90
7 purchase totals =	$901.77		$969.4537	$969.45	$969.50	$969.50