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	$14.98	3.443%	$15.4958	$15.50	$15.50	$15.50
Purchase #2	$139.77	13.466%	$158.5914	$158.59	$158.60	$158.60
Purchase #3	$78.98	12.291%	$88.6874	$88.69	$88.70	$88.70
Purchase #4	$131.59	12.447%	$147.969	$147.97	$147.95	$148.00
Purchase #5	$206.47	10.239%	$227.6105	$227.61	$227.60	$227.60
Purchase #6	$59.52	9.758%	$65.328	$65.33	$65.35	$65.30
Purchase #7	$238.41	12.131%	$267.3315	$267.33	$267.35	$267.30
7 purchase totals =	$869.72		$971.0136	$971.02	$971.05	$971.00