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	$39.27	8.463%	$42.5934	$42.59	$42.60	$42.60
Purchase #2	$125.97	10.340%	$138.9953	$139.00	$139.00	$139.00
Purchase #3	$85.82	4.103%	$89.3412	$89.34	$89.35	$89.30
Purchase #4	$9.47	5.434%	$9.9846	$9.98	$10.00	$10.00
Purchase #5	$191.37	4.116%	$199.2468	$199.25	$199.25	$199.20
Purchase #6	$94.64	12.201%	$106.187	$106.19	$106.20	$106.20
Purchase #7	$95.44	4.854%	$100.0727	$100.07	$100.05	$100.10
7 purchase totals =	$641.98		$686.4210	$686.42	$686.45	$686.40