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	$9.96	13.450%	$11.2996	$11.30	$11.30	$11.30
Purchase #2	$46.88	13.798%	$53.3485	$53.35	$53.35	$53.30
Purchase #3	$48.67	12.703%	$54.8526	$54.85	$54.85	$54.90
Purchase #4	$64.55	9.655%	$70.7823	$70.78	$70.80	$70.80
Purchase #5	$20.44	6.575%	$21.7839	$21.78	$21.80	$21.80
Purchase #6	$42.64	11.640%	$47.6033	$47.60	$47.60	$47.60
Purchase #7	$233.98	8.382%	$253.5922	$253.59	$253.60	$253.60
7 purchase totals =	$467.12		$513.2624	$513.25	$513.30	$513.30