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	$19.49	8.326%	$21.1127	$21.11	$21.10	$21.10
Purchase #2	$23.52	5.546%	$24.8244	$24.82	$24.80	$24.80
Purchase #3	$53.43	10.476%	$59.0273	$59.03	$59.05	$59.00
Purchase #4	$164.27	6.223%	$174.4925	$174.49	$174.50	$174.50
Purchase #5	$156.43	4.493%	$163.4584	$163.46	$163.45	$163.50
Purchase #6	$38.67	4.634%	$40.462	$40.46	$40.45	$40.50
Purchase #7	$82.94	9.160%	$90.5373	$90.54	$90.55	$90.50
7 purchase totals =	$538.75		$573.9146	$573.91	$573.90	$573.90