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	$30.76	5.232%	$32.3694	$32.37	$32.35	$32.40
Purchase #2	$181.92	9.342%	$198.915	$198.92	$198.90	$198.90
Purchase #3	$89.90	6.625%	$95.8559	$95.86	$95.85	$95.90
Purchase #4	$131.25	7.319%	$140.8562	$140.86	$140.85	$140.90
Purchase #5	$68.86	12.527%	$77.4861	$77.49	$77.50	$77.50
Purchase #6	$246.80	4.137%	$257.0101	$257.01	$257.00	$257.00
Purchase #7	$87.66	8.735%	$95.3171	$95.32	$95.30	$95.30
7 purchase totals =	$837.15		$897.8098	$897.83	$897.75	$897.90