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	$248.97	4.338%	$259.7703	$259.77	$259.75	$259.80
Purchase #2	$188.48	10.110%	$207.5353	$207.54	$207.55	$207.50
Purchase #3	$224.26	9.520%	$245.6096	$245.61	$245.60	$245.60
Purchase #4	$38.47	3.531%	$39.8284	$39.83	$39.85	$39.80
Purchase #5	$87.45	13.756%	$99.4796	$99.48	$99.50	$99.50
Purchase #6	$206.61	11.816%	$231.023	$231.02	$231.00	$231.00
Purchase #7	$37.32	8.828%	$40.6146	$40.61	$40.60	$40.60
7 purchase totals =	$1,031.56		$1,123.8608	$1,123.86	$1,123.85	$1,123.80