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	$91.60	9.766%	$100.5457	$100.55	$100.55	$100.50
Purchase #2	$76.60	9.693%	$84.0248	$84.02	$84.00	$84.00
Purchase #3	$44.93	3.636%	$46.5637	$46.56	$46.55	$46.60
Purchase #4	$133.89	3.349%	$138.374	$138.37	$138.35	$138.40
Purchase #5	$90.92	5.116%	$95.5715	$95.57	$95.55	$95.60
Purchase #6	$83.51	8.477%	$90.5891	$90.59	$90.60	$90.60
Purchase #7	$118.57	11.773%	$132.5292	$132.53	$132.55	$132.50
7 purchase totals =	$640.02		$688.1980	$688.19	$688.15	$688.20