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	$36.87	10.570%	$40.7672	$40.77	$40.75	$40.80
Purchase #2	$178.64	6.378%	$190.0337	$190.03	$190.05	$190.00
Purchase #3	$171.25	4.870%	$179.5899	$179.59	$179.60	$179.60
Purchase #4	$133.76	8.191%	$144.7163	$144.72	$144.70	$144.70
Purchase #5	$83.50	6.155%	$88.6394	$88.64	$88.65	$88.60
Purchase #6	$176.85	13.438%	$200.6151	$200.62	$200.60	$200.60
Purchase #7	$130.36	11.718%	$145.6356	$145.64	$145.65	$145.60
7 purchase totals =	$911.23		$989.9972	$990.01	$990.00	$989.90