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 $90.99   9.756%   $99.867   $99.87   $99.85   $99.90  
  Purchase #2 $127.51   10.455%   $140.8412   $140.84   $140.85   $140.80  
  Purchase #3 $61.80   12.247%   $69.3686   $69.37   $69.35   $69.40  
  Purchase #4 $31.30   12.643%   $35.2573   $35.26   $35.25   $35.30  
  Purchase #5 $219.59   6.374%   $233.5867   $233.59   $233.60   $233.60  
  Purchase #6 $95.39   13.364%   $108.1379   $108.14   $108.15   $108.10  
  Purchase #7 $163.41   8.857%   $177.8832   $177.88   $177.90   $177.90  
  7 purchase totals = $789.99       $864.9419   $864.95   $864.95   $865.00