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	$52.51	10.208%	$57.8702	$57.87	$57.85	$57.90
Purchase #2	$131.94	5.343%	$138.9896	$138.99	$139.00	$139.00
Purchase #3	$211.42	3.742%	$219.3313	$219.33	$219.35	$219.30
Purchase #4	$107.80	3.147%	$111.1925	$111.19	$111.20	$111.20
Purchase #5	$66.38	9.410%	$72.6264	$72.63	$72.65	$72.60
Purchase #6	$31.98	11.600%	$35.6897	$35.69	$35.70	$35.70
Purchase #7	$200.32	10.228%	$220.8087	$220.81	$220.80	$220.80
7 purchase totals =	$802.35		$856.5084	$856.51	$856.55	$856.50