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	$165.37	9.581%	$181.2141	$181.21	$181.20	$181.20
Purchase #2	$135.54	4.488%	$141.623	$141.62	$141.60	$141.60
Purchase #3	$108.69	13.406%	$123.261	$123.26	$123.25	$123.30
Purchase #4	$21.45	12.536%	$24.139	$24.14	$24.15	$24.10
Purchase #5	$112.61	10.827%	$124.8023	$124.80	$124.80	$124.80
Purchase #6	$42.31	13.179%	$47.886	$47.89	$47.90	$47.90
Purchase #7	$144.56	7.723%	$155.7244	$155.72	$155.70	$155.70
7 purchase totals =	$730.53		$798.6498	$798.64	$798.60	$798.60