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	$50.96	11.599%	$56.8709	$56.87	$56.85	$56.90
Purchase #2	$43.57	9.353%	$47.6451	$47.65	$47.65	$47.60
Purchase #3	$156.38	6.355%	$166.3179	$166.32	$166.30	$166.30
Purchase #4	$23.48	10.211%	$25.8775	$25.88	$25.90	$25.90
Purchase #5	$249.48	12.365%	$280.3282	$280.33	$280.35	$280.30
Purchase #6	$46.98	13.716%	$53.4238	$53.42	$53.40	$53.40
Purchase #7	$215.52	8.238%	$233.2745	$233.27	$233.25	$233.30
7 purchase totals =	$786.37		$863.7379	$863.74	$863.70	$863.70