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	$40.25	6.474%	$42.8558	$42.86	$42.85	$42.90
Purchase #2	$84.92	4.829%	$89.0208	$89.02	$89.00	$89.00
Purchase #3	$44.65	11.248%	$49.6722	$49.67	$49.65	$49.70
Purchase #4	$112.84	11.198%	$125.4758	$125.48	$125.50	$125.50
Purchase #5	$126.52	12.429%	$142.2452	$142.25	$142.25	$142.20
Purchase #6	$112.35	8.603%	$122.0155	$122.02	$122.00	$122.00
Purchase #7	$196.45	9.448%	$215.0106	$215.01	$215.00	$215.00
7 purchase totals =	$717.98		$786.2959	$786.31	$786.25	$786.30