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	$238.28	4.617%	$249.2814	$249.28	$249.30	$249.30
Purchase #2	$227.93	7.866%	$245.859	$245.86	$245.85	$245.90
Purchase #3	$182.79	5.284%	$192.4486	$192.45	$192.45	$192.40
Purchase #4	$8.87	12.841%	$10.009	$10.01	$10.00	$10.00
Purchase #5	$249.99	10.455%	$276.1265	$276.13	$276.15	$276.10
Purchase #6	$42.50	7.505%	$45.6896	$45.69	$45.70	$45.70
Purchase #7	$63.64	4.640%	$66.5929	$66.59	$66.60	$66.60
7 purchase totals =	$1,014.00		$1,086.0070	$1,086.01	$1,086.05	$1,086.00