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	$69.47	13.565%	$78.8936	$78.89	$78.90	$78.90
Purchase #2	$114.67	12.683%	$129.2136	$129.21	$129.20	$129.20
Purchase #3	$130.51	13.764%	$148.4734	$148.47	$148.45	$148.50
Purchase #4	$43.54	11.371%	$48.4909	$48.49	$48.50	$48.50
Purchase #5	$246.89	13.560%	$280.3683	$280.37	$280.35	$280.40
Purchase #6	$58.96	7.674%	$63.4846	$63.48	$63.50	$63.50
Purchase #7	$15.92	10.451%	$17.5838	$17.58	$17.60	$17.60
7 purchase totals =	$679.96		$766.5082	$766.49	$766.50	$766.60