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	$37.71	7.859%	$40.6736	$40.67	$40.65	$40.70
Purchase #2	$231.97	10.350%	$255.9789	$255.98	$256.00	$256.00
Purchase #3	$175.99	10.648%	$194.7294	$194.73	$194.75	$194.70
Purchase #4	$241.83	3.595%	$250.5238	$250.52	$250.50	$250.50
Purchase #5	$23.78	6.848%	$25.4085	$25.41	$25.40	$25.40
Purchase #6	$130.84	9.764%	$143.6152	$143.62	$143.60	$143.60
Purchase #7	$137.38	13.613%	$156.0815	$156.08	$156.10	$156.10
7 purchase totals =	$979.50		$1,067.0109	$1,067.01	$1,067.00	$1,067.00