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	$74.77	10.248%	$82.4324	$82.43	$82.45	$82.40
Purchase #2	$59.53	5.724%	$62.9375	$62.94	$62.95	$62.90
Purchase #3	$173.65	4.555%	$181.5598	$181.56	$181.55	$181.60
Purchase #4	$95.87	9.183%	$104.6737	$104.67	$104.65	$104.70
Purchase #5	$133.51	12.419%	$150.0906	$150.09	$150.10	$150.10
Purchase #6	$188.72	13.487%	$214.1727	$214.17	$214.15	$214.20
Purchase #7	$201.84	5.827%	$213.6012	$213.60	$213.60	$213.60
7 purchase totals =	$927.89		$1,009.4679	$1,009.46	$1,009.45	$1,009.50