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	$177.48	6.181%	$188.45	$188.45	$188.45	$188.50
Purchase #2	$33.86	8.702%	$36.8065	$36.81	$36.80	$36.80
Purchase #3	$87.27	3.583%	$90.3969	$90.40	$90.40	$90.40
Purchase #4	$47.48	11.392%	$52.8889	$52.89	$52.90	$52.90
Purchase #5	$237.71	8.341%	$257.5374	$257.54	$257.55	$257.50
Purchase #6	$40.55	3.332%	$41.9011	$41.90	$41.90	$41.90
Purchase #7	$225.31	4.569%	$235.6044	$235.60	$235.60	$235.60
7 purchase totals =	$849.66		$903.5852	$903.59	$903.60	$903.60