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	$231.78	11.579%	$258.6178	$258.62	$258.60	$258.60
Purchase #2	$246.77	13.656%	$280.4689	$280.47	$280.45	$280.50
Purchase #3	$145.76	11.620%	$162.6973	$162.70	$162.70	$162.70
Purchase #4	$133.70	10.195%	$147.3307	$147.33	$147.35	$147.30
Purchase #5	$111.38	4.199%	$116.0568	$116.06	$116.05	$116.10
Purchase #6	$88.62	13.434%	$100.5252	$100.53	$100.55	$100.50
Purchase #7	$39.38	13.504%	$44.6979	$44.70	$44.70	$44.70
7 purchase totals =	$997.39		$1,110.3946	$1,110.41	$1,110.40	$1,110.40