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	$126.76	3.346%	$131.0014	$131.00	$131.00	$131.00
Purchase #2	$44.60	13.158%	$50.4685	$50.47	$50.45	$50.50
Purchase #3	$94.94	5.688%	$100.3402	$100.34	$100.35	$100.30
Purchase #4	$199.46	6.180%	$211.7866	$211.79	$211.80	$211.80
Purchase #5	$159.98	5.514%	$168.8013	$168.80	$168.80	$168.80
Purchase #6	$68.90	13.759%	$78.38	$78.38	$78.40	$78.40
Purchase #7	$30.86	12.680%	$34.773	$34.77	$34.75	$34.80
7 purchase totals =	$725.50		$775.5510	$775.55	$775.55	$775.60