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	$248.85	12.748%	$280.5734	$280.57	$280.55	$280.60
Purchase #2	$54.87	5.429%	$57.8489	$57.85	$57.85	$57.80
Purchase #3	$69.43	13.177%	$78.5788	$78.58	$78.60	$78.60
Purchase #4	$176.49	3.382%	$182.4589	$182.46	$182.45	$182.50
Purchase #5	$203.65	10.815%	$225.6747	$225.67	$225.65	$225.70
Purchase #6	$143.60	11.359%	$159.9115	$159.91	$159.90	$159.90
Purchase #7	$122.96	3.322%	$127.0447	$127.04	$127.05	$127.00
7 purchase totals =	$1,019.85		$1,112.0909	$1,112.08	$1,112.05	$1,112.10