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	$69.78	12.478%	$78.4871	$78.49	$78.50	$78.50
Purchase #2	$119.84	10.432%	$132.3417	$132.34	$132.35	$132.30
Purchase #3	$162.42	5.212%	$170.8853	$170.89	$170.90	$170.90
Purchase #4	$20.86	13.311%	$23.6367	$23.64	$23.65	$23.60
Purchase #5	$57.49	3.618%	$59.57	$59.57	$59.55	$59.60
Purchase #6	$183.50	8.827%	$199.6975	$199.70	$199.70	$199.70
Purchase #7	$173.33	13.225%	$196.2529	$196.25	$196.25	$196.30
7 purchase totals =	$787.22		$860.8712	$860.88	$860.90	$860.90