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	$50.83	8.232%	$55.0143	$55.01	$55.00	$55.00
Purchase #2	$184.53	6.604%	$196.7164	$196.72	$196.70	$196.70
Purchase #3	$241.99	5.594%	$255.5269	$255.53	$255.55	$255.50
Purchase #4	$205.83	10.712%	$227.8785	$227.88	$227.90	$227.90
Purchase #5	$108.78	13.161%	$123.0965	$123.10	$123.10	$123.10
Purchase #6	$220.40	11.395%	$245.5146	$245.51	$245.50	$245.50
Purchase #7	$181.94	6.418%	$193.6169	$193.62	$193.60	$193.60
7 purchase totals =	$1,194.30		$1,297.3641	$1,297.37	$1,297.35	$1,297.30