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	$64.68	3.311%	$66.8216	$66.82	$66.80	$66.80
Purchase #2	$18.99	4.301%	$19.8068	$19.81	$19.80	$19.80
Purchase #3	$135.71	6.542%	$144.5881	$144.59	$144.60	$144.60
Purchase #4	$40.54	11.536%	$45.2167	$45.22	$45.20	$45.20
Purchase #5	$22.83	11.356%	$25.4226	$25.42	$25.40	$25.40
Purchase #6	$246.83	7.736%	$265.9248	$265.92	$265.90	$265.90
Purchase #7	$84.49	7.493%	$90.8208	$90.82	$90.80	$90.80
7 purchase totals =	$614.07		$658.6014	$658.60	$658.50	$658.50