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	$50.36	6.754%	$53.7613	$53.76	$53.75	$53.80
Purchase #2	$154.52	3.241%	$159.528	$159.53	$159.55	$159.50
Purchase #3	$132.87	7.725%	$143.1342	$143.13	$143.15	$143.10
Purchase #4	$103.43	5.860%	$109.491	$109.49	$109.50	$109.50
Purchase #5	$47.34	6.863%	$50.5889	$50.59	$50.60	$50.60
Purchase #6	$214.67	12.361%	$241.2054	$241.21	$241.20	$241.20
Purchase #7	$150.64	5.837%	$159.4329	$159.43	$159.45	$159.40
7 purchase totals =	$853.83		$917.1417	$917.14	$917.20	$917.10