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	$220.55	9.192%	$240.823	$240.82	$240.80	$240.80
Purchase #2	$159.47	6.533%	$169.8882	$169.89	$169.90	$169.90
Purchase #3	$111.81	6.137%	$118.6718	$118.67	$118.65	$118.70
Purchase #4	$111.60	10.279%	$123.0714	$123.07	$123.05	$123.10
Purchase #5	$56.81	7.752%	$61.2139	$61.21	$61.20	$61.20
Purchase #6	$94.29	6.864%	$100.7621	$100.76	$100.75	$100.80
Purchase #7	$75.63	11.771%	$84.5324	$84.53	$84.55	$84.50
7 purchase totals =	$830.16		$898.9628	$898.95	$898.90	$899.00