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	$248.89	12.631%	$280.3273	$280.33	$280.35	$280.30
Purchase #2	$79.82	13.295%	$90.4321	$90.43	$90.45	$90.40
Purchase #3	$156.48	6.418%	$166.5229	$166.52	$166.50	$166.50
Purchase #4	$119.96	13.732%	$136.4329	$136.43	$136.45	$136.40
Purchase #5	$198.75	8.294%	$215.2343	$215.23	$215.25	$215.20
Purchase #6	$164.77	11.405%	$183.562	$183.56	$183.55	$183.60
Purchase #7	$167.60	13.119%	$189.5874	$189.59	$189.60	$189.60
7 purchase totals =	$1,136.27		$1,262.0989	$1,262.09	$1,262.15	$1,262.00