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	$38.60	3.776%	$40.0575	$40.06	$40.05	$40.10
Purchase #2	$106.82	5.104%	$112.2721	$112.27	$112.25	$112.30
Purchase #3	$241.78	13.129%	$273.5233	$273.52	$273.50	$273.50
Purchase #4	$114.87	7.631%	$123.6357	$123.64	$123.65	$123.60
Purchase #5	$238.89	5.701%	$252.5091	$252.51	$252.50	$252.50
Purchase #6	$159.85	4.684%	$167.3374	$167.34	$167.35	$167.30
Purchase #7	$12.86	4.126%	$13.3906	$13.39	$13.40	$13.40
7 purchase totals =	$913.67		$982.7257	$982.73	$982.70	$982.70