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	$11.90	12.721%	$13.4138	$13.41	$13.40	$13.40
Purchase #2	$155.76	5.238%	$163.9187	$163.92	$163.90	$163.90
Purchase #3	$132.59	7.481%	$142.5091	$142.51	$142.50	$142.50
Purchase #4	$89.61	11.729%	$100.1204	$100.12	$100.10	$100.10
Purchase #5	$80.94	5.543%	$85.4265	$85.43	$85.45	$85.40
Purchase #6	$107.26	8.661%	$116.5498	$116.55	$116.55	$116.50
Purchase #7	$140.32	11.580%	$156.5691	$156.57	$156.55	$156.60
7 purchase totals =	$718.38		$778.5074	$778.51	$778.45	$778.40