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	$116.38	10.425%	$128.5126	$128.51	$128.50	$128.50
Purchase #2	$43.50	7.668%	$46.8356	$46.84	$46.85	$46.80
Purchase #3	$139.30	10.730%	$154.2469	$154.25	$154.25	$154.20
Purchase #4	$217.79	6.192%	$231.2756	$231.28	$231.30	$231.30
Purchase #5	$241.59	5.785%	$255.566	$255.57	$255.55	$255.60
Purchase #6	$154.54	8.364%	$167.4657	$167.47	$167.45	$167.50
Purchase #7	$123.48	6.738%	$131.8001	$131.80	$131.80	$131.80
7 purchase totals =	$1,036.58		$1,115.7025	$1,115.72	$1,115.70	$1,115.70