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	$35.63	13.597%	$40.4746	$40.47	$40.45	$40.50
Purchase #2	$137.49	3.509%	$142.3145	$142.31	$142.30	$142.30
Purchase #3	$133.48	7.194%	$143.0826	$143.08	$143.10	$143.10
Purchase #4	$247.90	13.271%	$280.7988	$280.80	$280.80	$280.80
Purchase #5	$160.95	8.512%	$174.6501	$174.65	$174.65	$174.70
Purchase #6	$175.46	3.344%	$181.3274	$181.33	$181.35	$181.30
Purchase #7	$231.87	9.317%	$253.4733	$253.47	$253.45	$253.50
7 purchase totals =	$1,122.78		$1,216.1213	$1,216.11	$1,216.10	$1,216.20