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	$53.25	7.127%	$57.0451	$57.05	$57.05	$57.00
Purchase #2	$181.86	13.146%	$205.7673	$205.77	$205.75	$205.80
Purchase #3	$106.88	13.323%	$121.1196	$121.12	$121.10	$121.10
Purchase #4	$66.82	8.429%	$72.4523	$72.45	$72.45	$72.50
Purchase #5	$163.28	3.412%	$168.8511	$168.85	$168.85	$168.90
Purchase #6	$191.57	3.383%	$198.0508	$198.05	$198.05	$198.10
Purchase #7	$63.98	4.696%	$66.9845	$66.98	$67.00	$67.00
7 purchase totals =	$827.64		$890.2707	$890.27	$890.25	$890.40