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	$38.78	9.715%	$42.5475	$42.55	$42.55	$42.50
Purchase #2	$82.70	3.588%	$85.6673	$85.67	$85.65	$85.70
Purchase #3	$179.42	5.490%	$189.2702	$189.27	$189.25	$189.30
Purchase #4	$69.59	3.293%	$71.8816	$71.88	$71.90	$71.90
Purchase #5	$36.64	12.247%	$41.1273	$41.13	$41.15	$41.10
Purchase #6	$182.36	5.333%	$192.0853	$192.09	$192.10	$192.10
Purchase #7	$19.88	3.382%	$20.5523	$20.55	$20.55	$20.60
7 purchase totals =	$609.37		$643.1315	$643.14	$643.15	$643.20