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	$34.70	9.228%	$37.9021	$37.90	$37.90	$37.90
Purchase #2	$214.94	3.182%	$221.7794	$221.78	$221.80	$221.80
Purchase #3	$96.67	9.533%	$105.8856	$105.89	$105.90	$105.90
Purchase #4	$171.29	3.610%	$177.4736	$177.47	$177.45	$177.50
Purchase #5	$37.63	7.301%	$40.3774	$40.38	$40.40	$40.40
Purchase #6	$151.70	5.175%	$159.5505	$159.55	$159.55	$159.60
Purchase #7	$102.97	8.699%	$111.9274	$111.93	$111.95	$111.90
7 purchase totals =	$809.90		$854.8960	$854.90	$854.95	$855.00