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	$246.43	4.411%	$257.3	$257.30	$257.30	$257.30
Purchase #2	$45.30	6.713%	$48.341	$48.34	$48.35	$48.30
Purchase #3	$41.74	7.496%	$44.8688	$44.87	$44.85	$44.90
Purchase #4	$143.47	5.582%	$151.4785	$151.48	$151.50	$151.50
Purchase #5	$105.82	3.779%	$109.8189	$109.82	$109.80	$109.80
Purchase #6	$244.50	11.761%	$273.2556	$273.26	$273.25	$273.30
Purchase #7	$31.90	9.305%	$34.8683	$34.87	$34.85	$34.90
7 purchase totals =	$859.16		$919.9311	$919.94	$919.90	$920.00