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	$247.72	5.139%	$260.4503	$260.45	$260.45	$260.50
Purchase #2	$132.92	6.664%	$141.7778	$141.78	$141.80	$141.80
Purchase #3	$250.41	11.874%	$280.1437	$280.14	$280.15	$280.10
Purchase #4	$241.95	8.470%	$262.4432	$262.44	$262.45	$262.40
Purchase #5	$249.31	12.724%	$281.0322	$281.03	$281.05	$281.00
Purchase #6	$59.76	10.387%	$65.9673	$65.97	$65.95	$66.00
Purchase #7	$127.38	13.673%	$144.7967	$144.80	$144.80	$144.80
7 purchase totals =	$1,309.45		$1,436.6112	$1,436.61	$1,436.65	$1,436.60