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	$248.43	4.479%	$259.5572	$259.56	$259.55	$259.60
Purchase #2	$82.35	10.553%	$91.0404	$91.04	$91.05	$91.00
Purchase #3	$132.83	3.865%	$137.9639	$137.96	$137.95	$138.00
Purchase #4	$44.83	13.304%	$50.7942	$50.79	$50.80	$50.80
Purchase #5	$79.47	12.577%	$89.4649	$89.46	$89.45	$89.50
Purchase #6	$205.47	4.637%	$214.9976	$215.00	$215.00	$215.00
Purchase #7	$103.60	5.108%	$108.8919	$108.89	$108.90	$108.90
7 purchase totals =	$896.98		$952.7101	$952.70	$952.70	$952.80