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	$38.78	4.864%	$40.6663	$40.67	$40.65	$40.70
Purchase #2	$183.30	5.238%	$192.9013	$192.90	$192.90	$192.90
Purchase #3	$137.60	5.308%	$144.9038	$144.90	$144.90	$144.90
Purchase #4	$36.90	9.508%	$40.4085	$40.41	$40.40	$40.40
Purchase #5	$170.92	8.555%	$185.5422	$185.54	$185.55	$185.50
Purchase #6	$231.29	3.553%	$239.5077	$239.51	$239.50	$239.50
Purchase #7	$200.98	6.448%	$213.9392	$213.94	$213.95	$213.90
7 purchase totals =	$999.77		$1,057.8690	$1,057.87	$1,057.85	$1,057.80