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	$60.55	9.164%	$66.0988	$66.10	$66.10	$66.10
Purchase #2	$236.79	11.520%	$264.0682	$264.07	$264.05	$264.10
Purchase #3	$154.83	12.690%	$174.4779	$174.48	$174.50	$174.50
Purchase #4	$63.71	12.641%	$71.7636	$71.76	$71.75	$71.80
Purchase #5	$61.76	12.587%	$69.5337	$69.53	$69.55	$69.50
Purchase #6	$62.49	3.849%	$64.8952	$64.90	$64.90	$64.90
Purchase #7	$132.41	13.333%	$150.0642	$150.06	$150.05	$150.10
7 purchase totals =	$772.54		$860.9016	$860.90	$860.90	$861.00