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	$40.91	13.222%	$46.3191	$46.32	$46.30	$46.30
Purchase #2	$99.56	10.500%	$110.0138	$110.01	$110.00	$110.00
Purchase #3	$187.40	6.510%	$199.5997	$199.60	$199.60	$199.60
Purchase #4	$190.54	4.725%	$199.543	$199.54	$199.55	$199.50
Purchase #5	$28.78	7.813%	$31.0286	$31.03	$31.05	$31.00
Purchase #6	$20.37	11.456%	$22.7036	$22.70	$22.70	$22.70
Purchase #7	$95.29	5.552%	$100.5805	$100.58	$100.60	$100.60
7 purchase totals =	$662.85		$709.7883	$709.78	$709.80	$709.70