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	$36.26	7.435%	$38.9559	$38.96	$38.95	$39.00
Purchase #2	$138.52	11.656%	$154.6659	$154.67	$154.65	$154.70
Purchase #3	$124.42	13.142%	$140.7713	$140.77	$140.75	$140.80
Purchase #4	$90.27	11.384%	$100.5463	$100.55	$100.55	$100.50
Purchase #5	$239.55	6.624%	$255.4178	$255.42	$255.40	$255.40
Purchase #6	$118.69	6.724%	$126.6707	$126.67	$126.65	$126.70
Purchase #7	$39.60	4.502%	$41.3828	$41.38	$41.40	$41.40
7 purchase totals =	$787.31		$858.4107	$858.42	$858.35	$858.50