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	$12.71	6.577%	$13.5459	$13.55	$13.55	$13.50
Purchase #2	$234.27	10.596%	$259.0932	$259.09	$259.10	$259.10
Purchase #3	$25.64	13.573%	$29.1201	$29.12	$29.10	$29.10
Purchase #4	$250.80	4.707%	$262.6052	$262.61	$262.60	$262.60
Purchase #5	$62.83	6.678%	$67.0258	$67.03	$67.05	$67.00
Purchase #6	$233.66	9.553%	$255.9815	$255.98	$256.00	$256.00
Purchase #7	$51.58	5.223%	$54.274	$54.27	$54.25	$54.30
7 purchase totals =	$871.49		$941.6457	$941.65	$941.65	$941.60