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	$246.78	13.842%	$280.9393	$280.94	$280.95	$280.90
Purchase #2	$207.38	10.811%	$229.7999	$229.80	$229.80	$229.80
Purchase #3	$89.81	11.384%	$100.034	$100.03	$100.05	$100.00
Purchase #4	$107.58	8.746%	$116.9889	$116.99	$117.00	$117.00
Purchase #5	$19.94	4.444%	$20.8261	$20.83	$20.85	$20.80
Purchase #6	$24.77	13.390%	$28.0867	$28.09	$28.10	$28.10
Purchase #7	$175.72	13.131%	$198.7938	$198.79	$198.80	$198.80
7 purchase totals =	$871.98		$975.4687	$975.47	$975.55	$975.40