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	$234.25	13.287%	$265.3748	$265.37	$265.35	$265.40
Purchase #2	$136.32	7.482%	$146.5195	$146.52	$146.50	$146.50
Purchase #3	$102.54	5.190%	$107.8618	$107.86	$107.85	$107.90
Purchase #4	$94.58	11.561%	$105.5144	$105.51	$105.50	$105.50
Purchase #5	$15.95	9.813%	$17.5152	$17.52	$17.50	$17.50
Purchase #6	$100.48	12.750%	$113.2912	$113.29	$113.30	$113.30
Purchase #7	$242.88	8.228%	$262.8642	$262.86	$262.85	$262.90
7 purchase totals =	$927.00		$1,018.9411	$1,018.93	$1,018.85	$1,019.00