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	$58.87	13.237%	$66.6626	$66.66	$66.65	$66.70
Purchase #2	$92.83	4.440%	$96.9517	$96.95	$96.95	$97.00
Purchase #3	$40.41	7.424%	$43.41	$43.41	$43.40	$43.40
Purchase #4	$11.30	5.293%	$11.8981	$11.90	$11.90	$11.90
Purchase #5	$95.53	9.493%	$104.5987	$104.60	$104.60	$104.60
Purchase #6	$162.53	3.636%	$168.4396	$168.44	$168.45	$168.40
Purchase #7	$47.53	8.455%	$51.5487	$51.55	$51.55	$51.50
7 purchase totals =	$509.00		$543.5094	$543.51	$543.50	$543.50