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	$125.34	11.436%	$139.6739	$139.67	$139.65	$139.70
Purchase #2	$60.98	8.599%	$66.2237	$66.22	$66.20	$66.20
Purchase #3	$111.69	10.507%	$123.4253	$123.43	$123.45	$123.40
Purchase #4	$67.57	13.142%	$76.45	$76.45	$76.45	$76.50
Purchase #5	$90.78	5.303%	$95.5941	$95.59	$95.60	$95.60
Purchase #6	$217.82	4.121%	$226.7964	$226.80	$226.80	$226.80
Purchase #7	$33.75	10.675%	$37.3528	$37.35	$37.35	$37.40
7 purchase totals =	$707.93		$765.5162	$765.51	$765.50	$765.60