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	$103.37	8.291%	$111.9404	$111.94	$111.95	$111.90
Purchase #2	$123.96	11.664%	$138.4187	$138.42	$138.40	$138.40
Purchase #3	$214.43	3.570%	$222.0852	$222.09	$222.10	$222.10
Purchase #4	$247.70	12.421%	$278.4668	$278.47	$278.45	$278.50
Purchase #5	$203.59	10.438%	$224.8407	$224.84	$224.85	$224.80
Purchase #6	$69.80	12.683%	$78.6527	$78.65	$78.65	$78.70
Purchase #7	$187.70	4.335%	$195.8368	$195.84	$195.85	$195.80
7 purchase totals =	$1,150.55		$1,250.2413	$1,250.25	$1,250.25	$1,250.20