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	$92.89	13.113%	$105.0707	$105.07	$105.05	$105.10
Purchase #2	$197.41	8.677%	$214.5393	$214.54	$214.55	$214.50
Purchase #3	$126.83	9.595%	$138.9993	$139.00	$139.00	$139.00
Purchase #4	$177.68	7.145%	$190.3752	$190.38	$190.40	$190.40
Purchase #5	$150.87	3.801%	$156.6046	$156.60	$156.60	$156.60
Purchase #6	$47.94	13.659%	$54.4881	$54.49	$54.50	$54.50
Purchase #7	$54.84	12.599%	$61.7493	$61.75	$61.75	$61.70
7 purchase totals =	$848.46		$921.8265	$921.83	$921.85	$921.80