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	$249.40	12.645%	$280.9366	$280.94	$280.95	$280.90
Purchase #2	$73.55	4.265%	$76.6869	$76.69	$76.70	$76.70
Purchase #3	$66.52	9.454%	$72.8088	$72.81	$72.80	$72.80
Purchase #4	$89.25	6.864%	$95.3761	$95.38	$95.40	$95.40
Purchase #5	$24.93	6.410%	$26.528	$26.53	$26.55	$26.50
Purchase #6	$48.43	10.861%	$53.69	$53.69	$53.70	$53.70
Purchase #7	$171.39	5.304%	$180.4805	$180.48	$180.50	$180.50
7 purchase totals =	$723.47		$786.5069	$786.52	$786.60	$786.50