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	$46.68	9.358%	$51.0483	$51.05	$51.05	$51.00
Purchase #2	$200.53	8.758%	$218.0924	$218.09	$218.10	$218.10
Purchase #3	$248.36	13.111%	$280.9225	$280.92	$280.90	$280.90
Purchase #4	$127.92	11.266%	$142.3315	$142.33	$142.35	$142.30
Purchase #5	$99.60	10.284%	$109.8429	$109.84	$109.85	$109.80
Purchase #6	$48.58	12.143%	$54.4791	$54.48	$54.50	$54.50
Purchase #7	$119.60	10.652%	$132.3398	$132.34	$132.35	$132.30
7 purchase totals =	$891.27		$989.0565	$989.05	$989.10	$988.90