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	$100.62	8.313%	$108.9845	$108.98	$109.00	$109.00
Purchase #2	$221.45	7.786%	$238.6921	$238.69	$238.70	$238.70
Purchase #3	$238.94	7.445%	$256.7291	$256.73	$256.75	$256.70
Purchase #4	$193.45	3.477%	$200.1763	$200.18	$200.20	$200.20
Purchase #5	$133.48	3.620%	$138.312	$138.31	$138.30	$138.30
Purchase #6	$38.89	9.145%	$42.4465	$42.45	$42.45	$42.40
Purchase #7	$122.73	12.801%	$138.4407	$138.44	$138.45	$138.40
7 purchase totals =	$1,049.56		$1,123.7812	$1,123.78	$1,123.85	$1,123.70