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	$10.70	6.715%	$11.4185	$11.42	$11.40	$11.40
Purchase #2	$22.45	13.466%	$25.4731	$25.47	$25.45	$25.50
Purchase #3	$95.64	5.615%	$101.0102	$101.01	$101.00	$101.00
Purchase #4	$66.87	8.870%	$72.8014	$72.80	$72.80	$72.80
Purchase #5	$199.56	11.400%	$222.3098	$222.31	$222.30	$222.30
Purchase #6	$17.37	6.491%	$18.4975	$18.50	$18.50	$18.50
Purchase #7	$178.44	12.331%	$200.4434	$200.44	$200.45	$200.40
7 purchase totals =	$591.03		$651.9539	$651.95	$651.90	$651.90