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	$14.36	8.419%	$15.569	$15.57	$15.55	$15.60
Purchase #2	$136.79	3.783%	$141.9648	$141.96	$141.95	$142.00
Purchase #3	$201.54	6.622%	$214.886	$214.89	$214.90	$214.90
Purchase #4	$84.49	5.433%	$89.0803	$89.08	$89.10	$89.10
Purchase #5	$78.83	6.207%	$83.723	$83.72	$83.70	$83.70
Purchase #6	$145.61	8.802%	$158.4266	$158.43	$158.45	$158.40
Purchase #7	$18.59	9.166%	$20.294	$20.29	$20.30	$20.30
7 purchase totals =	$680.21		$723.9437	$723.94	$723.95	$724.00