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	$93.48	9.854%	$102.6915	$102.69	$102.70	$102.70
Purchase #2	$159.62	3.299%	$164.8859	$164.89	$164.90	$164.90
Purchase #3	$134.89	4.620%	$141.1219	$141.12	$141.10	$141.10
Purchase #4	$46.35	11.326%	$51.5996	$51.60	$51.60	$51.60
Purchase #5	$73.90	8.184%	$79.948	$79.95	$79.95	$79.90
Purchase #6	$47.65	12.320%	$53.5205	$53.52	$53.50	$53.50
Purchase #7	$84.52	7.403%	$90.777	$90.78	$90.80	$90.80
7 purchase totals =	$640.41		$684.5444	$684.55	$684.55	$684.50