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	$225.65	13.561%	$256.2504	$256.25	$256.25	$256.30
Purchase #2	$157.61	12.413%	$177.1741	$177.17	$177.15	$177.20
Purchase #3	$82.83	3.248%	$85.5203	$85.52	$85.50	$85.50
Purchase #4	$83.70	8.187%	$90.5525	$90.55	$90.55	$90.60
Purchase #5	$139.25	13.432%	$157.9541	$157.95	$157.95	$158.00
Purchase #6	$11.59	7.281%	$12.4339	$12.43	$12.45	$12.40
Purchase #7	$34.72	12.396%	$39.0239	$39.02	$39.00	$39.00
7 purchase totals =	$735.35		$818.9092	$818.89	$818.85	$819.00