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	$34.29	10.774%	$37.9844	$37.98	$38.00	$38.00
Purchase #2	$34.58	11.431%	$38.5328	$38.53	$38.55	$38.50
Purchase #3	$175.48	8.742%	$190.8205	$190.82	$190.80	$190.80
Purchase #4	$212.79	8.789%	$231.4921	$231.49	$231.50	$231.50
Purchase #5	$73.39	9.793%	$80.5771	$80.58	$80.60	$80.60
Purchase #6	$91.37	13.800%	$103.9791	$103.98	$104.00	$104.00
Purchase #7	$6.87	8.383%	$7.4459	$7.45	$7.45	$7.40
7 purchase totals =	$628.77		$690.8319	$690.83	$690.90	$690.80