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	$82.90	5.493%	$87.4537	$87.45	$87.45	$87.50
Purchase #2	$126.54	13.404%	$143.5014	$143.50	$143.50	$143.50
Purchase #3	$57.81	13.656%	$65.7045	$65.70	$65.70	$65.70
Purchase #4	$108.36	5.769%	$114.6113	$114.61	$114.60	$114.60
Purchase #5	$35.36	6.786%	$37.7595	$37.76	$37.75	$37.80
Purchase #6	$76.29	9.266%	$83.359	$83.36	$83.35	$83.40
Purchase #7	$126.44	8.775%	$137.5351	$137.54	$137.55	$137.50
7 purchase totals =	$613.70		$669.9245	$669.92	$669.90	$670.00