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	$143.65	8.192%	$155.4178	$155.42	$155.40	$155.40
Purchase #2	$111.37	11.714%	$124.4159	$124.42	$124.40	$124.40
Purchase #3	$80.95	7.394%	$86.9354	$86.94	$86.95	$86.90
Purchase #4	$83.65	5.770%	$88.4766	$88.48	$88.50	$88.50
Purchase #5	$132.90	4.818%	$139.3031	$139.30	$139.30	$139.30
Purchase #6	$64.61	3.375%	$66.7906	$66.79	$66.80	$66.80
Purchase #7	$50.35	8.266%	$54.5119	$54.51	$54.50	$54.50
7 purchase totals =	$667.48		$715.8513	$715.86	$715.85	$715.80