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	$141.64	11.661%	$158.1566	$158.16	$158.15	$158.20
Purchase #2	$108.87	9.705%	$119.4358	$119.44	$119.45	$119.40
Purchase #3	$207.63	3.293%	$214.4673	$214.47	$214.45	$214.50
Purchase #4	$140.55	6.757%	$150.047	$150.05	$150.05	$150.00
Purchase #5	$68.83	13.792%	$78.323	$78.32	$78.30	$78.30
Purchase #6	$155.27	11.533%	$173.1773	$173.18	$173.20	$173.20
Purchase #7	$26.54	5.134%	$27.9026	$27.90	$27.90	$27.90
7 purchase totals =	$849.33		$921.5096	$921.52	$921.50	$921.50