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	$90.85	9.274%	$99.2754	$99.28	$99.30	$99.30
Purchase #2	$133.35	9.746%	$146.3463	$146.35	$146.35	$146.30
Purchase #3	$70.43	3.438%	$72.8514	$72.85	$72.85	$72.90
Purchase #4	$64.28	3.439%	$66.4906	$66.49	$66.50	$66.50
Purchase #5	$226.57	12.568%	$255.0453	$255.05	$255.05	$255.00
Purchase #6	$83.88	6.526%	$89.354	$89.35	$89.35	$89.40
Purchase #7	$217.52	5.742%	$230.01	$230.01	$230.00	$230.00
7 purchase totals =	$886.88		$959.3730	$959.38	$959.40	$959.40