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	$133.57	3.872%	$138.7418	$138.74	$138.75	$138.70
Purchase #2	$150.62	13.667%	$171.2052	$171.21	$171.20	$171.20
Purchase #3	$25.82	12.721%	$29.1046	$29.10	$29.10	$29.10
Purchase #4	$233.83	10.271%	$257.8467	$257.85	$257.85	$257.80
Purchase #5	$71.37	9.326%	$78.026	$78.03	$78.05	$78.00
Purchase #6	$90.81	11.111%	$100.8999	$100.90	$100.90	$100.90
Purchase #7	$212.69	4.208%	$221.64	$221.64	$221.65	$221.60
7 purchase totals =	$918.71		$997.4642	$997.47	$997.50	$997.30