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	$20.48	8.421%	$22.2046	$22.20	$22.20	$22.20
Purchase #2	$199.85	12.822%	$225.4748	$225.47	$225.45	$225.50
Purchase #3	$83.89	8.142%	$90.7203	$90.72	$90.70	$90.70
Purchase #4	$11.69	7.259%	$12.5386	$12.54	$12.55	$12.50
Purchase #5	$19.82	5.186%	$20.8479	$20.85	$20.85	$20.80
Purchase #6	$133.31	8.614%	$144.7933	$144.79	$144.80	$144.80
Purchase #7	$214.37	6.535%	$228.3791	$228.38	$228.40	$228.40
7 purchase totals =	$683.41		$744.9586	$744.95	$744.95	$744.90