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	$53.51	5.669%	$56.5435	$56.54	$56.55	$56.50
Purchase #2	$69.60	13.380%	$78.9125	$78.91	$78.90	$78.90
Purchase #3	$177.30	8.239%	$191.9077	$191.91	$191.90	$191.90
Purchase #4	$44.81	11.183%	$49.8211	$49.82	$49.80	$49.80
Purchase #5	$181.72	13.715%	$206.6429	$206.64	$206.65	$206.60
Purchase #6	$164.71	6.773%	$175.8658	$175.87	$175.85	$175.90
Purchase #7	$213.94	5.523%	$225.7559	$225.76	$225.75	$225.80
7 purchase totals =	$905.59		$985.4494	$985.45	$985.40	$985.40