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	$100.65	12.132%	$112.8609	$112.86	$112.85	$112.90
Purchase #2	$13.94	8.110%	$15.0705	$15.07	$15.05	$15.10
Purchase #3	$112.89	4.427%	$117.8876	$117.89	$117.90	$117.90
Purchase #4	$78.51	5.117%	$82.5274	$82.53	$82.55	$82.50
Purchase #5	$81.64	9.622%	$89.4954	$89.50	$89.50	$89.50
Purchase #6	$20.86	13.712%	$23.7203	$23.72	$23.70	$23.70
Purchase #7	$89.57	9.163%	$97.7773	$97.78	$97.80	$97.80
7 purchase totals =	$498.06		$539.3394	$539.35	$539.35	$539.40