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	$132.67	10.195%	$146.1957	$146.20	$146.20	$146.20
Purchase #2	$18.94	13.119%	$21.4247	$21.42	$21.40	$21.40
Purchase #3	$124.94	7.287%	$134.0444	$134.04	$134.05	$134.00
Purchase #4	$131.52	12.548%	$148.0231	$148.02	$148.00	$148.00
Purchase #5	$61.79	5.215%	$65.0123	$65.01	$65.00	$65.00
Purchase #6	$38.62	9.576%	$42.3183	$42.32	$42.30	$42.30
Purchase #7	$100.42	5.426%	$105.8688	$105.87	$105.85	$105.90
7 purchase totals =	$608.90		$662.8873	$662.88	$662.80	$662.80