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	$90.26	5.779%	$95.4761	$95.48	$95.50	$95.50
Purchase #2	$153.89	8.858%	$167.5216	$167.52	$167.50	$167.50
Purchase #3	$137.88	9.661%	$151.2006	$151.20	$151.20	$151.20
Purchase #4	$177.72	8.568%	$192.947	$192.95	$192.95	$192.90
Purchase #5	$116.41	3.754%	$120.78	$120.78	$120.80	$120.80
Purchase #6	$25.39	8.342%	$27.508	$27.51	$27.50	$27.50
Purchase #7	$219.38	10.247%	$241.8599	$241.86	$241.85	$241.90
7 purchase totals =	$920.93		$997.2932	$997.30	$997.30	$997.30