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	$127.80	10.520%	$141.2446	$141.24	$141.25	$141.20
Purchase #2	$75.78	9.565%	$83.0284	$83.03	$83.05	$83.00
Purchase #3	$244.72	11.284%	$272.3342	$272.33	$272.35	$272.30
Purchase #4	$138.62	10.505%	$153.182	$153.18	$153.20	$153.20
Purchase #5	$82.49	4.160%	$85.9216	$85.92	$85.90	$85.90
Purchase #6	$99.60	11.527%	$111.0809	$111.08	$111.10	$111.10
Purchase #7	$31.60	5.694%	$33.3993	$33.40	$33.40	$33.40
7 purchase totals =	$800.61		$880.1910	$880.18	$880.25	$880.10