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	$80.88	8.208%	$87.5186	$87.52	$87.50	$87.50
Purchase #2	$201.51	12.654%	$227.0091	$227.01	$227.00	$227.00
Purchase #3	$247.28	13.520%	$280.7123	$280.71	$280.70	$280.70
Purchase #4	$51.47	3.684%	$53.3662	$53.37	$53.35	$53.40
Purchase #5	$73.73	3.788%	$76.5229	$76.52	$76.50	$76.50
Purchase #6	$131.57	6.161%	$139.676	$139.68	$139.70	$139.70
Purchase #7	$59.38	12.281%	$66.6725	$66.67	$66.65	$66.70
7 purchase totals =	$845.82		$931.4776	$931.48	$931.40	$931.50