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	$101.73	10.583%	$112.4961	$112.50	$112.50	$112.50
Purchase #2	$48.37	12.176%	$54.2595	$54.26	$54.25	$54.30
Purchase #3	$56.72	12.809%	$63.9853	$63.99	$64.00	$64.00
Purchase #4	$118.89	10.695%	$131.6053	$131.61	$131.60	$131.60
Purchase #5	$27.42	4.689%	$28.7057	$28.71	$28.70	$28.70
Purchase #6	$175.48	13.699%	$199.519	$199.52	$199.50	$199.50
Purchase #7	$59.58	11.256%	$66.2863	$66.29	$66.30	$66.30
7 purchase totals =	$588.19		$656.8572	$656.88	$656.85	$656.90