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	$51.52	10.706%	$57.0357	$57.04	$57.05	$57.00
Purchase #2	$139.48	7.578%	$150.0498	$150.05	$150.05	$150.00
Purchase #3	$123.41	8.868%	$134.354	$134.35	$134.35	$134.40
Purchase #4	$137.87	3.581%	$142.8071	$142.81	$142.80	$142.80
Purchase #5	$131.77	10.725%	$145.9023	$145.90	$145.90	$145.90
Purchase #6	$108.34	13.799%	$123.2898	$123.29	$123.30	$123.30
Purchase #7	$222.68	10.646%	$246.3865	$246.39	$246.40	$246.40
7 purchase totals =	$915.07		$999.8252	$999.83	$999.85	$999.80