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	$24.52	12.553%	$27.598	$27.60	$27.60	$27.60
Purchase #2	$219.38	9.195%	$239.552	$239.55	$239.55	$239.60
Purchase #3	$92.52	11.189%	$102.8721	$102.87	$102.85	$102.90
Purchase #4	$196.30	7.767%	$211.5466	$211.55	$211.55	$211.50
Purchase #5	$83.76	9.371%	$91.6091	$91.61	$91.60	$91.60
Purchase #6	$246.78	3.501%	$255.4198	$255.42	$255.40	$255.40
Purchase #7	$10.86	13.661%	$12.3436	$12.34	$12.35	$12.30
7 purchase totals =	$874.12		$940.9412	$940.94	$940.90	$940.90