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	$40.93	6.356%	$43.5315	$43.53	$43.55	$43.50
Purchase #2	$165.97	8.836%	$180.6351	$180.64	$180.65	$180.60
Purchase #3	$100.56	3.456%	$104.0354	$104.04	$104.05	$104.00
Purchase #4	$142.90	12.517%	$160.7868	$160.79	$160.80	$160.80
Purchase #5	$100.45	12.311%	$112.8164	$112.82	$112.80	$112.80
Purchase #6	$158.81	4.621%	$166.1486	$166.15	$166.15	$166.10
Purchase #7	$182.35	12.632%	$205.3845	$205.38	$205.40	$205.40
7 purchase totals =	$891.97		$973.3383	$973.35	$973.40	$973.20