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	$231.27	10.441%	$255.4169	$255.42	$255.40	$255.40
Purchase #2	$128.38	12.670%	$144.6457	$144.65	$144.65	$144.60
Purchase #3	$51.51	5.418%	$54.3008	$54.30	$54.30	$54.30
Purchase #4	$103.60	4.791%	$108.5635	$108.56	$108.55	$108.60
Purchase #5	$186.45	9.418%	$204.0099	$204.01	$204.00	$204.00
Purchase #6	$113.90	9.505%	$124.7262	$124.73	$124.75	$124.70
Purchase #7	$135.76	9.601%	$148.7943	$148.79	$148.80	$148.80
7 purchase totals =	$950.87		$1,040.4573	$1,040.46	$1,040.45	$1,040.40