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	$83.79	3.328%	$86.5785	$86.58	$86.60	$86.60
Purchase #2	$113.44	13.265%	$128.4878	$128.49	$128.50	$128.50
Purchase #3	$161.84	6.748%	$172.761	$172.76	$172.75	$172.80
Purchase #4	$96.35	8.410%	$104.453	$104.45	$104.45	$104.50
Purchase #5	$71.29	13.536%	$80.9398	$80.94	$80.95	$80.90
Purchase #6	$16.66	10.809%	$18.4608	$18.46	$18.45	$18.50
Purchase #7	$25.31	10.106%	$27.8678	$27.87	$27.85	$27.90
7 purchase totals =	$568.68		$619.5487	$619.55	$619.55	$619.70