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	$49.99	11.854%	$55.9158	$55.92	$55.90	$55.90
Purchase #2	$141.94	11.724%	$158.581	$158.58	$158.60	$158.60
Purchase #3	$237.80	11.625%	$265.4443	$265.44	$265.45	$265.40
Purchase #4	$53.71	10.576%	$59.3904	$59.39	$59.40	$59.40
Purchase #5	$104.64	9.789%	$114.8832	$114.88	$114.90	$114.90
Purchase #6	$91.91	9.342%	$100.4962	$100.50	$100.50	$100.50
Purchase #7	$75.75	11.631%	$84.5605	$84.56	$84.55	$84.60
7 purchase totals =	$755.74		$839.2714	$839.27	$839.30	$839.30