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	$241.27	6.362%	$256.6196	$256.62	$256.60	$256.60
Purchase #2	$95.66	7.542%	$102.8747	$102.87	$102.85	$102.90
Purchase #3	$144.48	11.111%	$160.5332	$160.53	$160.55	$160.50
Purchase #4	$166.78	7.758%	$179.7188	$179.72	$179.70	$179.70
Purchase #5	$47.93	13.746%	$54.5185	$54.52	$54.50	$54.50
Purchase #6	$119.80	5.240%	$126.0775	$126.08	$126.10	$126.10
Purchase #7	$155.38	4.289%	$162.0442	$162.04	$162.05	$162.00
7 purchase totals =	$971.30		$1,042.3865	$1,042.38	$1,042.35	$1,042.30