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	$29.39	7.802%	$31.683	$31.68	$31.70	$31.70
Purchase #2	$177.86	9.182%	$194.1911	$194.19	$194.20	$194.20
Purchase #3	$135.48	4.703%	$141.8516	$141.85	$141.85	$141.90
Purchase #4	$225.59	3.311%	$233.0593	$233.06	$233.05	$233.10
Purchase #5	$235.87	11.278%	$262.4714	$262.47	$262.45	$262.50
Purchase #6	$104.25	7.590%	$112.1626	$112.16	$112.15	$112.20
Purchase #7	$12.45	11.354%	$13.8636	$13.86	$13.85	$13.90
7 purchase totals =	$920.89		$989.2826	$989.27	$989.25	$989.50