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	$79.47	10.500%	$87.8144	$87.81	$87.80	$87.80
Purchase #2	$241.61	3.238%	$249.4333	$249.43	$249.45	$249.40
Purchase #3	$117.43	12.328%	$131.9068	$131.91	$131.90	$131.90
Purchase #4	$97.53	9.232%	$106.534	$106.53	$106.55	$106.50
Purchase #5	$116.71	5.848%	$123.5352	$123.54	$123.55	$123.50
Purchase #6	$11.51	13.657%	$13.0819	$13.08	$13.10	$13.10
Purchase #7	$105.80	11.398%	$117.8591	$117.86	$117.85	$117.90
7 purchase totals =	$770.06		$830.1647	$830.16	$830.20	$830.10