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	$78.58	4.124%	$81.8206	$81.82	$81.80	$81.80
Purchase #2	$227.76	12.224%	$255.6014	$255.60	$255.60	$255.60
Purchase #3	$133.71	7.831%	$144.1808	$144.18	$144.20	$144.20
Purchase #4	$137.93	5.447%	$145.443	$145.44	$145.45	$145.40
Purchase #5	$80.54	7.338%	$86.45	$86.45	$86.45	$86.50
Purchase #6	$114.36	8.145%	$123.6746	$123.67	$123.65	$123.70
Purchase #7	$243.94	7.177%	$261.4476	$261.45	$261.45	$261.40
7 purchase totals =	$1,016.82		$1,098.6180	$1,098.61	$1,098.60	$1,098.60