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	$66.92	9.684%	$73.4005	$73.40	$73.40	$73.40
Purchase #2	$91.72	8.572%	$99.5822	$99.58	$99.60	$99.60
Purchase #3	$242.64	10.793%	$268.8281	$268.83	$268.85	$268.80
Purchase #4	$8.87	12.659%	$9.9929	$9.99	$10.00	$10.00
Purchase #5	$20.50	4.785%	$21.4809	$21.48	$21.50	$21.50
Purchase #6	$61.84	4.874%	$64.8541	$64.85	$64.85	$64.90
Purchase #7	$83.47	7.872%	$90.0408	$90.04	$90.05	$90.00
7 purchase totals =	$575.96		$628.1795	$628.17	$628.25	$628.20