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	$20.52	4.445%	$21.4321	$21.43	$21.45	$21.40
Purchase #2	$98.47	10.383%	$108.6941	$108.69	$108.70	$108.70
Purchase #3	$38.51	10.401%	$42.5154	$42.52	$42.50	$42.50
Purchase #4	$7.25	7.859%	$7.8198	$7.82	$7.80	$7.80
Purchase #5	$123.29	4.538%	$128.8849	$128.88	$128.90	$128.90
Purchase #6	$77.77	8.768%	$84.5889	$84.59	$84.60	$84.60
Purchase #7	$217.84	3.238%	$224.8937	$224.89	$224.90	$224.90
7 purchase totals =	$583.65		$618.8289	$618.82	$618.85	$618.80