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	$19.54	9.479%	$21.3922	$21.39	$21.40	$21.40
Purchase #2	$91.73	13.318%	$103.9466	$103.95	$103.95	$103.90
Purchase #3	$63.55	12.244%	$71.3311	$71.33	$71.35	$71.30
Purchase #4	$132.64	12.223%	$148.8526	$148.85	$148.85	$148.90
Purchase #5	$167.95	7.573%	$180.6689	$180.67	$180.65	$180.70
Purchase #6	$190.47	5.211%	$200.3954	$200.40	$200.40	$200.40
Purchase #7	$233.94	10.230%	$257.8721	$257.87	$257.85	$257.90
7 purchase totals =	$899.82		$984.4589	$984.46	$984.45	$984.50