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	$243.89	6.156%	$258.9039	$258.90	$258.90	$258.90
Purchase #2	$187.29	10.228%	$206.446	$206.45	$206.45	$206.40
Purchase #3	$80.32	6.244%	$85.3352	$85.34	$85.35	$85.30
Purchase #4	$137.42	6.689%	$146.612	$146.61	$146.60	$146.60
Purchase #5	$25.54	7.682%	$27.502	$27.50	$27.50	$27.50
Purchase #6	$13.32	12.564%	$14.9935	$14.99	$15.00	$15.00
Purchase #7	$83.71	9.810%	$91.922	$91.92	$91.90	$91.90
7 purchase totals =	$771.49		$831.7146	$831.71	$831.70	$831.60