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	$142.61	13.357%	$161.6584	$161.66	$161.65	$161.70
Purchase #2	$33.87	13.838%	$38.5569	$38.56	$38.55	$38.60
Purchase #3	$126.97	7.822%	$136.9016	$136.90	$136.90	$136.90
Purchase #4	$140.65	10.109%	$154.8683	$154.87	$154.85	$154.90
Purchase #5	$249.72	5.724%	$264.014	$264.01	$264.00	$264.00
Purchase #6	$83.52	6.762%	$89.1676	$89.17	$89.15	$89.20
Purchase #7	$132.97	6.366%	$141.4349	$141.43	$141.45	$141.40
7 purchase totals =	$910.31		$986.6017	$986.60	$986.55	$986.70