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	$238.78	4.509%	$249.5466	$249.55	$249.55	$249.50
Purchase #2	$223.92	11.570%	$249.8275	$249.83	$249.85	$249.80
Purchase #3	$61.35	3.326%	$63.3905	$63.39	$63.40	$63.40
Purchase #4	$250.55	7.860%	$270.2432	$270.24	$270.25	$270.20
Purchase #5	$37.61	12.766%	$42.4113	$42.41	$42.40	$42.40
Purchase #6	$78.74	6.828%	$84.1164	$84.12	$84.10	$84.10
Purchase #7	$40.45	5.365%	$42.6201	$42.62	$42.60	$42.60
7 purchase totals =	$931.40		$1,002.1556	$1,002.16	$1,002.15	$1,002.00