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	$209.27	6.514%	$222.9018	$222.90	$222.90	$222.90
Purchase #2	$109.45	12.291%	$122.9025	$122.90	$122.90	$122.90
Purchase #3	$97.81	10.854%	$108.4263	$108.43	$108.45	$108.40
Purchase #4	$191.93	13.260%	$217.3799	$217.38	$217.40	$217.40
Purchase #5	$86.55	12.387%	$97.2709	$97.27	$97.25	$97.30
Purchase #6	$106.57	9.579%	$116.7783	$116.78	$116.80	$116.80
Purchase #7	$196.60	10.802%	$217.8367	$217.84	$217.85	$217.80
7 purchase totals =	$998.18		$1,103.4964	$1,103.50	$1,103.55	$1,103.50