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	$19.34	9.767%	$21.2289	$21.23	$21.25	$21.20
Purchase #2	$102.48	13.243%	$116.0514	$116.05	$116.05	$116.10
Purchase #3	$84.43	6.767%	$90.1434	$90.14	$90.15	$90.10
Purchase #4	$215.29	9.164%	$235.0192	$235.02	$235.00	$235.00
Purchase #5	$108.94	3.426%	$112.6723	$112.67	$112.65	$112.70
Purchase #6	$83.79	8.141%	$90.6113	$90.61	$90.60	$90.60
Purchase #7	$15.59	9.414%	$17.0576	$17.06	$17.05	$17.10
7 purchase totals =	$629.86		$682.7841	$682.78	$682.75	$682.80