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	$61.81	9.749%	$67.8359	$67.84	$67.85	$67.80
Purchase #2	$214.44	5.806%	$226.8904	$226.89	$226.90	$226.90
Purchase #3	$114.45	11.389%	$127.4847	$127.48	$127.50	$127.50
Purchase #4	$36.52	12.107%	$40.9415	$40.94	$40.95	$40.90
Purchase #5	$76.59	10.763%	$84.8334	$84.83	$84.85	$84.80
Purchase #6	$191.68	10.412%	$211.6377	$211.64	$211.65	$211.60
Purchase #7	$83.55	7.422%	$89.7511	$89.75	$89.75	$89.80
7 purchase totals =	$779.04		$849.3747	$849.37	$849.45	$849.30