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	$134.26	6.357%	$142.7949	$142.79	$142.80	$142.80
Purchase #2	$192.54	12.669%	$216.9329	$216.93	$216.95	$216.90
Purchase #3	$42.39	8.327%	$45.9198	$45.92	$45.90	$45.90
Purchase #4	$214.60	12.373%	$241.1525	$241.15	$241.15	$241.20
Purchase #5	$198.85	8.365%	$215.4838	$215.48	$215.50	$215.50
Purchase #6	$164.72	7.351%	$176.8286	$176.83	$176.85	$176.80
Purchase #7	$94.49	4.480%	$98.7232	$98.72	$98.70	$98.70
7 purchase totals =	$1,041.85		$1,137.8357	$1,137.82	$1,137.85	$1,137.80