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	$55.75	6.172%	$59.1909	$59.19	$59.20	$59.20
Purchase #2	$174.38	12.696%	$196.5193	$196.52	$196.50	$196.50
Purchase #3	$72.45	5.661%	$76.5514	$76.55	$76.55	$76.60
Purchase #4	$47.82	3.387%	$49.4397	$49.44	$49.45	$49.40
Purchase #5	$129.31	6.788%	$138.0876	$138.09	$138.10	$138.10
Purchase #6	$126.81	7.795%	$136.6948	$136.69	$136.70	$136.70
Purchase #7	$145.60	8.216%	$157.5625	$157.56	$157.55	$157.60
7 purchase totals =	$752.12		$814.0462	$814.04	$814.05	$814.10