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	$133.57	4.440%	$139.5005	$139.50	$139.50	$139.50
Purchase #2	$101.64	4.186%	$105.8947	$105.89	$105.90	$105.90
Purchase #3	$23.57	9.351%	$25.774	$25.77	$25.75	$25.80
Purchase #4	$181.48	5.206%	$190.9278	$190.93	$190.95	$190.90
Purchase #5	$213.91	8.232%	$231.5191	$231.52	$231.50	$231.50
Purchase #6	$153.29	7.385%	$164.6105	$164.61	$164.60	$164.60
Purchase #7	$159.55	12.675%	$179.773	$179.77	$179.75	$179.80
7 purchase totals =	$967.01		$1,037.9996	$1,037.99	$1,037.95	$1,038.00