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	$72.69	8.420%	$78.8105	$78.81	$78.80	$78.80
Purchase #2	$134.32	7.504%	$144.3994	$144.40	$144.40	$144.40
Purchase #3	$49.47	12.113%	$55.4623	$55.46	$55.45	$55.50
Purchase #4	$139.47	10.215%	$153.7169	$153.72	$153.70	$153.70
Purchase #5	$55.88	6.546%	$59.5379	$59.54	$59.55	$59.50
Purchase #6	$155.52	11.768%	$173.8216	$173.82	$173.80	$173.80
Purchase #7	$220.96	8.583%	$239.925	$239.93	$239.95	$239.90
7 purchase totals =	$828.31		$905.6736	$905.68	$905.65	$905.60