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	$246.78	9.397%	$269.9699	$269.97	$269.95	$270.00
Purchase #2	$57.51	11.237%	$63.9724	$63.97	$63.95	$64.00
Purchase #3	$195.45	13.320%	$221.4839	$221.48	$221.50	$221.50
Purchase #4	$248.98	12.790%	$280.8245	$280.82	$280.80	$280.80
Purchase #5	$187.57	12.305%	$210.6505	$210.65	$210.65	$210.70
Purchase #6	$39.32	10.789%	$43.5622	$43.56	$43.55	$43.60
Purchase #7	$97.72	12.452%	$109.8881	$109.89	$109.90	$109.90
7 purchase totals =	$1,073.33		$1,200.3515	$1,200.34	$1,200.30	$1,200.50