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	$123.52	13.678%	$140.4151	$140.42	$140.40	$140.40
Purchase #2	$33.78	6.330%	$35.9183	$35.92	$35.90	$35.90
Purchase #3	$144.88	12.850%	$163.4971	$163.50	$163.50	$163.50
Purchase #4	$172.59	4.158%	$179.7663	$179.77	$179.75	$179.80
Purchase #5	$84.59	9.458%	$92.5905	$92.59	$92.60	$92.60
Purchase #6	$6.81	4.847%	$7.1401	$7.14	$7.15	$7.10
Purchase #7	$133.99	6.105%	$142.1701	$142.17	$142.15	$142.20
7 purchase totals =	$700.16		$761.4975	$761.51	$761.45	$761.50