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	$90.94	9.491%	$99.5711	$99.57	$99.55	$99.60
Purchase #2	$246.48	13.751%	$280.3735	$280.37	$280.35	$280.40
Purchase #3	$193.61	7.699%	$208.516	$208.52	$208.50	$208.50
Purchase #4	$126.88	6.872%	$135.5992	$135.60	$135.60	$135.60
Purchase #5	$81.61	10.266%	$89.9881	$89.99	$90.00	$90.00
Purchase #6	$12.62	7.809%	$13.6055	$13.61	$13.60	$13.60
Purchase #7	$118.64	12.786%	$133.8093	$133.81	$133.80	$133.80
7 purchase totals =	$870.78		$961.4627	$961.47	$961.40	$961.50