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	$59.71	11.471%	$66.5593	$66.56	$66.55	$66.60
Purchase #2	$133.31	11.752%	$148.9766	$148.98	$149.00	$149.00
Purchase #3	$47.90	8.284%	$51.868	$51.87	$51.85	$51.90
Purchase #4	$48.85	3.419%	$50.5202	$50.52	$50.50	$50.50
Purchase #5	$178.87	3.470%	$185.0768	$185.08	$185.10	$185.10
Purchase #6	$200.30	5.304%	$210.9239	$210.92	$210.90	$210.90
Purchase #7	$168.59	4.231%	$175.723	$175.72	$175.70	$175.70
7 purchase totals =	$837.53		$889.6478	$889.65	$889.60	$889.70