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	$236.78	12.575%	$266.5551	$266.56	$266.55	$266.60
Purchase #2	$104.35	13.181%	$118.1044	$118.10	$118.10	$118.10
Purchase #3	$95.67	10.136%	$105.3671	$105.37	$105.35	$105.40
Purchase #4	$92.35	12.402%	$103.8032	$103.80	$103.80	$103.80
Purchase #5	$136.37	11.672%	$152.2871	$152.29	$152.30	$152.30
Purchase #6	$162.35	11.546%	$181.0949	$181.09	$181.10	$181.10
Purchase #7	$231.77	13.395%	$262.8156	$262.82	$262.80	$262.80
7 purchase totals =	$1,059.64		$1,190.0274	$1,190.03	$1,190.00	$1,190.10