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	$12.85	7.469%	$13.8098	$13.81	$13.80	$13.80
Purchase #2	$119.52	3.247%	$123.4008	$123.40	$123.40	$123.40
Purchase #3	$136.79	3.271%	$141.2644	$141.26	$141.25	$141.30
Purchase #4	$125.47	4.689%	$131.3533	$131.35	$131.35	$131.40
Purchase #5	$111.30	7.276%	$119.3982	$119.40	$119.40	$119.40
Purchase #6	$95.51	7.777%	$102.9378	$102.94	$102.95	$102.90
Purchase #7	$16.77	8.104%	$18.129	$18.13	$18.15	$18.10
7 purchase totals =	$618.21		$650.2933	$650.29	$650.30	$650.30