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	$109.61	5.504%	$115.6429	$115.64	$115.65	$115.60
Purchase #2	$181.29	4.422%	$189.3066	$189.31	$189.30	$189.30
Purchase #3	$161.77	13.625%	$183.8112	$183.81	$183.80	$183.80
Purchase #4	$126.85	9.271%	$138.6103	$138.61	$138.60	$138.60
Purchase #5	$95.30	5.373%	$100.4205	$100.42	$100.40	$100.40
Purchase #6	$73.58	12.672%	$82.9041	$82.90	$82.90	$82.90
Purchase #7	$242.50	5.264%	$255.2652	$255.27	$255.25	$255.30
7 purchase totals =	$990.90		$1,065.9608	$1,065.96	$1,065.90	$1,065.90