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	$230.25	11.191%	$256.0173	$256.02	$256.00	$256.00
Purchase #2	$192.57	8.124%	$208.2144	$208.21	$208.20	$208.20
Purchase #3	$82.77	4.381%	$86.3962	$86.40	$86.40	$86.40
Purchase #4	$83.78	9.248%	$91.528	$91.53	$91.55	$91.50
Purchase #5	$150.93	8.811%	$164.2284	$164.23	$164.25	$164.20
Purchase #6	$132.74	10.854%	$147.1476	$147.15	$147.15	$147.10
Purchase #7	$184.35	3.782%	$191.3221	$191.32	$191.30	$191.30
7 purchase totals =	$1,057.39		$1,144.8540	$1,144.86	$1,144.85	$1,144.70