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	$76.37	9.757%	$83.8214	$83.82	$83.80	$83.80
Purchase #2	$200.76	7.840%	$216.4996	$216.50	$216.50	$216.50
Purchase #3	$126.59	11.860%	$141.6036	$141.60	$141.60	$141.60
Purchase #4	$72.51	5.291%	$76.3465	$76.35	$76.35	$76.30
Purchase #5	$156.75	11.711%	$175.107	$175.11	$175.10	$175.10
Purchase #6	$49.75	3.356%	$51.4196	$51.42	$51.40	$51.40
Purchase #7	$127.51	13.584%	$144.831	$144.83	$144.85	$144.80
7 purchase totals =	$810.24		$889.6287	$889.63	$889.60	$889.50