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	$53.98	4.682%	$56.5073	$56.51	$56.50	$56.50
Purchase #2	$231.45	10.367%	$255.4444	$255.44	$255.45	$255.40
Purchase #3	$45.35	6.719%	$48.3971	$48.40	$48.40	$48.40
Purchase #4	$24.49	4.731%	$25.6486	$25.65	$25.65	$25.60
Purchase #5	$27.81	9.338%	$30.4069	$30.41	$30.40	$30.40
Purchase #6	$136.71	5.606%	$144.374	$144.37	$144.35	$144.40
Purchase #7	$62.67	6.700%	$66.8689	$66.87	$66.85	$66.90
7 purchase totals =	$582.46		$627.6472	$627.65	$627.60	$627.60