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	$32.64	11.457%	$36.3796	$36.38	$36.40	$36.40
Purchase #2	$60.78	7.390%	$65.2716	$65.27	$65.25	$65.30
Purchase #3	$57.26	3.471%	$59.2475	$59.25	$59.25	$59.20
Purchase #4	$56.86	11.287%	$63.2778	$63.28	$63.30	$63.30
Purchase #5	$151.86	13.187%	$171.8858	$171.89	$171.90	$171.90
Purchase #6	$78.62	7.735%	$84.7013	$84.70	$84.70	$84.70
Purchase #7	$171.71	7.317%	$184.274	$184.27	$184.25	$184.30
7 purchase totals =	$609.73		$665.0376	$665.04	$665.05	$665.10