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	$104.96	6.578%	$111.8643	$111.86	$111.85	$111.90
Purchase #2	$149.58	3.378%	$154.6328	$154.63	$154.65	$154.60
Purchase #3	$21.46	11.434%	$23.9137	$23.91	$23.90	$23.90
Purchase #4	$60.81	10.618%	$67.2668	$67.27	$67.25	$67.30
Purchase #5	$246.94	13.732%	$280.8498	$280.85	$280.85	$280.80
Purchase #6	$89.59	8.333%	$97.0555	$97.06	$97.05	$97.10
Purchase #7	$79.64	3.542%	$82.4608	$82.46	$82.45	$82.50
7 purchase totals =	$752.98		$818.0437	$818.04	$818.00	$818.10