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	$239.32	8.241%	$259.0424	$259.04	$259.05	$259.00
Purchase #2	$7.84	11.165%	$8.7153	$8.72	$8.70	$8.70
Purchase #3	$51.57	9.119%	$56.2727	$56.27	$56.25	$56.30
Purchase #4	$73.37	7.428%	$78.8199	$78.82	$78.80	$78.80
Purchase #5	$137.97	10.515%	$152.4775	$152.48	$152.50	$152.50
Purchase #6	$100.29	11.309%	$111.6318	$111.63	$111.65	$111.60
Purchase #7	$97.83	8.792%	$106.4312	$106.43	$106.45	$106.40
7 purchase totals =	$708.19		$773.3908	$773.39	$773.40	$773.30