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	$47.92	11.597%	$53.4773	$53.48	$53.50	$53.50
Purchase #2	$174.60	6.790%	$186.4553	$186.46	$186.45	$186.50
Purchase #3	$89.84	3.126%	$92.6484	$92.65	$92.65	$92.60
Purchase #4	$8.64	10.437%	$9.5418	$9.54	$9.55	$9.50
Purchase #5	$106.77	10.386%	$117.8591	$117.86	$117.85	$117.90
Purchase #6	$66.90	8.177%	$72.3704	$72.37	$72.35	$72.40
Purchase #7	$164.88	13.617%	$187.3317	$187.33	$187.35	$187.30
7 purchase totals =	$659.55		$719.6840	$719.69	$719.70	$719.70