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	$35.33	13.694%	$40.1681	$40.17	$40.15	$40.20
Purchase #2	$165.88	8.110%	$179.3329	$179.33	$179.35	$179.30
Purchase #3	$248.75	5.459%	$262.3293	$262.33	$262.35	$262.30
Purchase #4	$137.82	3.452%	$142.5775	$142.58	$142.60	$142.60
Purchase #5	$47.80	6.854%	$51.0762	$51.08	$51.10	$51.10
Purchase #6	$53.71	3.297%	$55.4808	$55.48	$55.50	$55.50
Purchase #7	$134.29	3.536%	$139.0385	$139.04	$139.05	$139.00
7 purchase totals =	$823.58		$870.0033	$870.01	$870.10	$870.00