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	$139.84	6.442%	$148.8485	$148.85	$148.85	$148.80
Purchase #2	$95.56	12.446%	$107.4534	$107.45	$107.45	$107.50
Purchase #3	$247.87	13.154%	$280.4748	$280.47	$280.45	$280.50
Purchase #4	$134.38	10.154%	$148.0249	$148.02	$148.00	$148.00
Purchase #5	$112.27	8.790%	$122.1385	$122.14	$122.15	$122.10
Purchase #6	$105.87	12.527%	$119.1323	$119.13	$119.15	$119.10
Purchase #7	$142.57	12.779%	$160.789	$160.79	$160.80	$160.80
7 purchase totals =	$978.36		$1,086.8614	$1,086.85	$1,086.85	$1,086.80