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	$155.64	13.456%	$176.5829	$176.58	$176.60	$176.60
Purchase #2	$220.42	9.676%	$241.7478	$241.75	$241.75	$241.70
Purchase #3	$52.71	12.273%	$59.1791	$59.18	$59.20	$59.20
Purchase #4	$31.53	5.167%	$33.1592	$33.16	$33.15	$33.20
Purchase #5	$39.82	5.679%	$42.0814	$42.08	$42.10	$42.10
Purchase #6	$150.45	13.218%	$170.3365	$170.34	$170.35	$170.30
Purchase #7	$98.68	10.533%	$109.074	$109.07	$109.05	$109.10
7 purchase totals =	$749.25		$832.1609	$832.16	$832.20	$832.20