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	$50.39	9.645%	$55.2501	$55.25	$55.25	$55.30
Purchase #2	$40.77	12.864%	$46.0147	$46.01	$46.00	$46.00
Purchase #3	$132.99	3.257%	$137.3215	$137.32	$137.30	$137.30
Purchase #4	$6.99	3.737%	$7.2512	$7.25	$7.25	$7.30
Purchase #5	$90.27	13.497%	$102.4537	$102.45	$102.45	$102.50
Purchase #6	$10.54	12.729%	$11.8816	$11.88	$11.90	$11.90
Purchase #7	$142.83	11.471%	$159.214	$159.21	$159.20	$159.20
7 purchase totals =	$474.78		$519.3868	$519.37	$519.35	$519.50