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	$66.88	12.841%	$75.4681	$75.47	$75.45	$75.50
Purchase #2	$80.66	11.314%	$89.7859	$89.79	$89.80	$89.80
Purchase #3	$239.82	4.464%	$250.5256	$250.53	$250.55	$250.50
Purchase #4	$25.81	8.503%	$28.0046	$28.00	$28.00	$28.00
Purchase #5	$53.53	11.493%	$59.6822	$59.68	$59.70	$59.70
Purchase #6	$231.79	12.207%	$260.0846	$260.08	$260.10	$260.10
Purchase #7	$196.55	9.636%	$215.4896	$215.49	$215.50	$215.50
7 purchase totals =	$895.04		$979.0406	$979.04	$979.10	$979.10