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	$15.48	5.540%	$16.3376	$16.34	$16.35	$16.30
Purchase #2	$80.57	3.373%	$83.2876	$83.29	$83.30	$83.30
Purchase #3	$50.38	3.716%	$52.2521	$52.25	$52.25	$52.30
Purchase #4	$153.52	12.580%	$172.8328	$172.83	$172.85	$172.80
Purchase #5	$151.32	11.766%	$169.1243	$169.12	$169.10	$169.10
Purchase #6	$114.72	7.422%	$123.2345	$123.23	$123.25	$123.20
Purchase #7	$144.60	3.208%	$149.2388	$149.24	$149.25	$149.20
7 purchase totals =	$710.59		$766.3077	$766.30	$766.35	$766.20