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	$79.81	6.285%	$84.8261	$84.83	$84.85	$84.80
Purchase #2	$183.55	9.249%	$200.5265	$200.53	$200.55	$200.50
Purchase #3	$41.58	13.196%	$47.0669	$47.07	$47.05	$47.10
Purchase #4	$111.37	11.797%	$124.5083	$124.51	$124.50	$124.50
Purchase #5	$128.35	6.554%	$136.7621	$136.76	$136.75	$136.80
Purchase #6	$219.63	4.488%	$229.487	$229.49	$229.50	$229.50
Purchase #7	$240.70	6.205%	$255.6354	$255.64	$255.65	$255.60
7 purchase totals =	$1,004.99		$1,078.8123	$1,078.83	$1,078.85	$1,078.80