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	$6.76	10.852%	$7.4936	$7.49	$7.50	$7.50
Purchase #2	$243.90	4.652%	$255.2462	$255.25	$255.25	$255.20
Purchase #3	$176.53	13.536%	$200.4251	$200.43	$200.45	$200.40
Purchase #4	$249.74	12.132%	$280.0385	$280.04	$280.05	$280.00
Purchase #5	$13.83	12.480%	$15.556	$15.56	$15.55	$15.60
Purchase #6	$6.86	7.294%	$7.3604	$7.36	$7.35	$7.40
Purchase #7	$103.75	10.567%	$114.7133	$114.71	$114.70	$114.70
7 purchase totals =	$801.37		$880.8331	$880.84	$880.85	$880.80