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	$43.70	11.697%	$48.8116	$48.81	$48.80	$48.80
Purchase #2	$63.46	12.612%	$71.4636	$71.46	$71.45	$71.50
Purchase #3	$244.43	3.545%	$253.095	$253.10	$253.10	$253.10
Purchase #4	$52.90	9.559%	$57.9567	$57.96	$57.95	$58.00
Purchase #5	$24.61	11.172%	$27.3594	$27.36	$27.35	$27.40
Purchase #6	$150.72	12.682%	$169.8343	$169.83	$169.85	$169.80
Purchase #7	$35.98	5.843%	$38.0823	$38.08	$38.10	$38.10
7 purchase totals =	$615.80		$666.6029	$666.60	$666.60	$666.70