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	$127.72	9.185%	$139.4511	$139.45	$139.45	$139.50
Purchase #2	$246.63	6.622%	$262.9618	$262.96	$262.95	$263.00
Purchase #3	$20.30	4.462%	$21.2058	$21.21	$21.20	$21.20
Purchase #4	$52.79	10.834%	$58.5093	$58.51	$58.50	$58.50
Purchase #5	$123.43	4.180%	$128.5894	$128.59	$128.60	$128.60
Purchase #6	$80.77	11.749%	$90.2597	$90.26	$90.25	$90.30
Purchase #7	$18.53	5.341%	$19.5197	$19.52	$19.50	$19.50
7 purchase totals =	$670.17		$720.4968	$720.50	$720.45	$720.60