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	$136.90	5.593%	$144.5568	$144.56	$144.55	$144.60
Purchase #2	$186.79	11.719%	$208.6799	$208.68	$208.70	$208.70
Purchase #3	$218.60	10.421%	$241.3803	$241.38	$241.40	$241.40
Purchase #4	$203.50	7.337%	$218.4308	$218.43	$218.45	$218.40
Purchase #5	$18.81	6.175%	$19.9715	$19.97	$19.95	$20.00
Purchase #6	$43.51	4.506%	$45.4706	$45.47	$45.45	$45.50
Purchase #7	$36.45	9.804%	$40.0236	$40.02	$40.00	$40.00
7 purchase totals =	$844.56		$918.5135	$918.51	$918.50	$918.60