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	$12.33	12.512%	$13.8727	$13.87	$13.85	$13.90
Purchase #2	$133.87	8.126%	$144.7483	$144.75	$144.75	$144.70
Purchase #3	$51.99	7.167%	$55.7161	$55.72	$55.70	$55.70
Purchase #4	$193.86	12.643%	$218.3697	$218.37	$218.35	$218.40
Purchase #5	$61.30	10.660%	$67.8346	$67.83	$67.85	$67.80
Purchase #6	$129.94	11.265%	$144.5777	$144.58	$144.60	$144.60
Purchase #7	$174.81	13.767%	$198.8761	$198.88	$198.90	$198.90
7 purchase totals =	$758.10		$843.9952	$844.00	$844.00	$844.00