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	$39.31	10.456%	$43.4203	$43.42	$43.40	$43.40
Purchase #2	$36.78	11.363%	$40.9593	$40.96	$40.95	$41.00
Purchase #3	$202.30	6.512%	$215.4738	$215.47	$215.45	$215.50
Purchase #4	$168.27	8.166%	$182.0109	$182.01	$182.00	$182.00
Purchase #5	$95.47	5.274%	$100.5051	$100.51	$100.50	$100.50
Purchase #6	$19.71	10.724%	$21.8237	$21.82	$21.80	$21.80
Purchase #7	$194.31	10.629%	$214.9632	$214.96	$214.95	$215.00
7 purchase totals =	$756.15		$819.1563	$819.15	$819.05	$819.20