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	$33.43	9.388%	$36.5684	$36.57	$36.55	$36.60
Purchase #2	$133.85	13.597%	$152.0496	$152.05	$152.05	$152.00
Purchase #3	$65.25	11.336%	$72.6467	$72.65	$72.65	$72.60
Purchase #4	$138.25	10.590%	$152.8907	$152.89	$152.90	$152.90
Purchase #5	$57.38	10.350%	$63.3188	$63.32	$63.30	$63.30
Purchase #6	$42.53	9.770%	$46.6852	$46.69	$46.70	$46.70
Purchase #7	$59.27	12.354%	$66.5922	$66.59	$66.60	$66.60
7 purchase totals =	$529.96		$590.7516	$590.76	$590.75	$590.70