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	$105.57	10.316%	$116.4606	$116.46	$116.45	$116.50
Purchase #2	$215.71	6.770%	$230.3136	$230.31	$230.30	$230.30
Purchase #3	$164.54	3.533%	$170.3532	$170.35	$170.35	$170.40
Purchase #4	$178.47	4.300%	$186.1442	$186.14	$186.15	$186.10
Purchase #5	$215.45	3.861%	$223.7685	$223.77	$223.75	$223.80
Purchase #6	$47.45	7.574%	$51.0439	$51.04	$51.05	$51.00
Purchase #7	$84.29	12.494%	$94.8212	$94.82	$94.80	$94.80
7 purchase totals =	$1,011.48		$1,072.9052	$1,072.89	$1,072.85	$1,072.90