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	$119.95	13.849%	$136.5619	$136.56	$136.55	$136.60
Purchase #2	$221.63	5.827%	$234.5444	$234.54	$234.55	$234.50
Purchase #3	$206.95	3.458%	$214.1063	$214.11	$214.10	$214.10
Purchase #4	$32.41	7.585%	$34.8683	$34.87	$34.85	$34.90
Purchase #5	$31.83	10.856%	$35.2855	$35.29	$35.30	$35.30
Purchase #6	$75.72	3.623%	$78.4633	$78.46	$78.45	$78.50
Purchase #7	$59.88	11.179%	$66.574	$66.57	$66.55	$66.60
7 purchase totals =	$748.37		$800.4037	$800.40	$800.35	$800.50