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	$228.42	6.333%	$242.8858	$242.89	$242.90	$242.90
Purchase #2	$240.75	12.470%	$270.7715	$270.77	$270.75	$270.80
Purchase #3	$210.50	7.589%	$226.4748	$226.47	$226.45	$226.50
Purchase #4	$118.80	4.127%	$123.7029	$123.70	$123.70	$123.70
Purchase #5	$60.77	6.487%	$64.7121	$64.71	$64.70	$64.70
Purchase #6	$182.27	9.632%	$199.8262	$199.83	$199.85	$199.80
Purchase #7	$136.42	4.442%	$142.4798	$142.48	$142.50	$142.50
7 purchase totals =	$1,177.93		$1,270.8531	$1,270.85	$1,270.85	$1,270.90