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	$63.85	6.394%	$67.9326	$67.93	$67.95	$67.90
Purchase #2	$107.91	11.687%	$120.5214	$120.52	$120.50	$120.50
Purchase #3	$248.40	12.757%	$280.0884	$280.09	$280.10	$280.10
Purchase #4	$119.87	5.857%	$126.8908	$126.89	$126.90	$126.90
Purchase #5	$208.82	6.208%	$221.7835	$221.78	$221.80	$221.80
Purchase #6	$48.34	7.296%	$51.8669	$51.87	$51.85	$51.90
Purchase #7	$133.37	13.389%	$151.2269	$151.23	$151.25	$151.20
7 purchase totals =	$930.56		$1,020.3105	$1,020.31	$1,020.35	$1,020.30