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	$39.37	13.481%	$44.6775	$44.68	$44.70	$44.70
Purchase #2	$109.68	11.130%	$121.8874	$121.89	$121.90	$121.90
Purchase #3	$248.83	12.777%	$280.623	$280.62	$280.60	$280.60
Purchase #4	$37.72	9.658%	$41.363	$41.36	$41.35	$41.40
Purchase #5	$62.75	6.623%	$66.9059	$66.91	$66.90	$66.90
Purchase #6	$39.26	8.613%	$42.6415	$42.64	$42.65	$42.60
Purchase #7	$41.54	4.177%	$43.2751	$43.28	$43.30	$43.30
7 purchase totals =	$579.15		$641.3734	$641.38	$641.40	$641.40