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	$96.86	10.593%	$107.1204	$107.12	$107.10	$107.10
Purchase #2	$45.68	11.858%	$51.0967	$51.10	$51.10	$51.10
Purchase #3	$89.72	9.545%	$98.2838	$98.28	$98.30	$98.30
Purchase #4	$127.84	11.769%	$142.8855	$142.89	$142.90	$142.90
Purchase #5	$32.93	4.210%	$34.3164	$34.32	$34.30	$34.30
Purchase #6	$220.25	4.125%	$229.3353	$229.34	$229.35	$229.30
Purchase #7	$140.60	13.461%	$159.5262	$159.53	$159.55	$159.50
7 purchase totals =	$753.88		$822.5643	$822.58	$822.60	$822.50