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	$89.86	13.682%	$102.1546	$102.15	$102.15	$102.20
Purchase #2	$133.60	4.389%	$139.4637	$139.46	$139.45	$139.50
Purchase #3	$40.83	9.127%	$44.5566	$44.56	$44.55	$44.60
Purchase #4	$115.59	4.323%	$120.587	$120.59	$120.60	$120.60
Purchase #5	$13.73	12.466%	$15.4416	$15.44	$15.45	$15.40
Purchase #6	$231.34	11.105%	$257.0303	$257.03	$257.05	$257.00
Purchase #7	$247.83	4.615%	$259.2674	$259.27	$259.25	$259.30
7 purchase totals =	$872.78		$938.5012	$938.50	$938.50	$938.60