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	$109.77	9.452%	$120.1455	$120.15	$120.15	$120.10
Purchase #2	$130.60	4.388%	$136.3307	$136.33	$136.35	$136.30
Purchase #3	$161.40	4.373%	$168.458	$168.46	$168.45	$168.50
Purchase #4	$165.69	10.204%	$182.597	$182.60	$182.60	$182.60
Purchase #5	$87.51	8.866%	$95.2686	$95.27	$95.25	$95.30
Purchase #6	$142.49	11.267%	$158.5443	$158.54	$158.55	$158.50
Purchase #7	$41.68	5.337%	$43.9045	$43.90	$43.90	$43.90
7 purchase totals =	$839.14		$905.2486	$905.25	$905.25	$905.20