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	$11.35	13.124%	$12.8396	$12.84	$12.85	$12.80
Purchase #2	$7.47	4.534%	$7.8087	$7.81	$7.80	$7.80
Purchase #3	$45.37	12.116%	$50.867	$50.87	$50.85	$50.90
Purchase #4	$212.66	8.575%	$230.8956	$230.90	$230.90	$230.90
Purchase #5	$92.30	3.393%	$95.4317	$95.43	$95.45	$95.40
Purchase #6	$194.62	11.542%	$217.083	$217.08	$217.10	$217.10
Purchase #7	$59.75	4.671%	$62.5409	$62.54	$62.55	$62.50
7 purchase totals =	$623.52		$677.4665	$677.47	$677.50	$677.40