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	$80.55	12.341%	$90.4907	$90.49	$90.50	$90.50
Purchase #2	$54.48	13.624%	$61.9024	$61.90	$61.90	$61.90
Purchase #3	$214.55	5.178%	$225.6594	$225.66	$225.65	$225.70
Purchase #4	$109.46	12.667%	$123.3253	$123.33	$123.35	$123.30
Purchase #5	$26.62	3.622%	$27.5842	$27.58	$27.60	$27.60
Purchase #6	$166.26	9.193%	$181.5443	$181.54	$181.55	$181.50
Purchase #7	$135.76	3.438%	$140.4274	$140.43	$140.45	$140.40
7 purchase totals =	$787.68		$850.9337	$850.93	$851.00	$850.90