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	$222.91	11.466%	$248.4689	$248.47	$248.45	$248.50
Purchase #2	$36.47	10.770%	$40.3978	$40.40	$40.40	$40.40
Purchase #3	$100.69	11.709%	$112.4798	$112.48	$112.50	$112.50
Purchase #4	$157.79	13.535%	$179.1469	$179.15	$179.15	$179.10
Purchase #5	$132.56	7.763%	$142.8506	$142.85	$142.85	$142.90
Purchase #6	$11.29	3.392%	$11.673	$11.67	$11.65	$11.70
Purchase #7	$194.65	8.638%	$211.4639	$211.46	$211.45	$211.50
7 purchase totals =	$856.36		$946.4809	$946.48	$946.45	$946.60