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	$243.93	10.509%	$269.5646	$269.56	$269.55	$269.60
Purchase #2	$240.59	8.446%	$260.9102	$260.91	$260.90	$260.90
Purchase #3	$166.67	9.742%	$182.907	$182.91	$182.90	$182.90
Purchase #4	$72.48	8.710%	$78.793	$78.79	$78.80	$78.80
Purchase #5	$54.30	11.781%	$60.6971	$60.70	$60.70	$60.70
Purchase #6	$112.27	6.244%	$119.2801	$119.28	$119.30	$119.30
Purchase #7	$20.69	3.824%	$21.4812	$21.48	$21.50	$21.50
7 purchase totals =	$910.93		$993.6332	$993.63	$993.65	$993.70