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	$40.53	3.766%	$42.0564	$42.06	$42.05	$42.10
Purchase #2	$89.57	13.358%	$101.5348	$101.53	$101.55	$101.50
Purchase #3	$35.45	4.624%	$37.0892	$37.09	$37.10	$37.10
Purchase #4	$247.62	13.105%	$280.0706	$280.07	$280.05	$280.10
Purchase #5	$128.86	5.704%	$136.2102	$136.21	$136.20	$136.20
Purchase #6	$100.40	6.463%	$106.8889	$106.89	$106.90	$106.90
Purchase #7	$208.32	11.201%	$231.6539	$231.65	$231.65	$231.70
7 purchase totals =	$850.75		$935.5040	$935.50	$935.50	$935.60