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	$241.60	7.191%	$258.9735	$258.97	$258.95	$259.00
Purchase #2	$107.86	8.565%	$117.0982	$117.10	$117.10	$117.10
Purchase #3	$74.96	4.789%	$78.5498	$78.55	$78.55	$78.50
Purchase #4	$39.26	7.654%	$42.265	$42.27	$42.25	$42.30
Purchase #5	$245.86	3.867%	$255.3674	$255.37	$255.35	$255.40
Purchase #6	$83.83	10.382%	$92.5332	$92.53	$92.55	$92.50
Purchase #7	$62.78	6.484%	$66.8507	$66.85	$66.85	$66.90
7 purchase totals =	$856.15		$911.6378	$911.64	$911.60	$911.70