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	$46.60	10.574%	$51.5275	$51.53	$51.55	$51.50
Purchase #2	$147.54	4.652%	$154.4036	$154.40	$154.40	$154.40
Purchase #3	$195.35	10.158%	$215.1937	$215.19	$215.20	$215.20
Purchase #4	$246.72	13.523%	$280.0839	$280.08	$280.10	$280.10
Purchase #5	$188.51	5.813%	$199.4681	$199.47	$199.45	$199.50
Purchase #6	$244.96	13.445%	$277.8949	$277.89	$277.90	$277.90
Purchase #7	$10.72	10.751%	$11.8725	$11.87	$11.85	$11.90
7 purchase totals =	$1,080.40		$1,190.4442	$1,190.43	$1,190.45	$1,190.50