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 $55.32   8.380%   $59.9558   $59.96   $59.95   $60.00  
  Purchase #2 $168.75   12.831%   $190.4023   $190.40   $190.40   $190.40  
  Purchase #3 $129.51   6.358%   $137.7442   $137.74   $137.75   $137.70  
  Purchase #4 $240.80   7.131%   $257.9714   $257.97   $257.95   $258.00  
  Purchase #5 $41.61   8.195%   $45.0199   $45.02   $45.00   $45.00  
  Purchase #6 $19.53   13.495%   $22.1656   $22.17   $22.15   $22.20  
  Purchase #7 $144.91   4.811%   $151.8816   $151.88   $151.90   $151.90  
  7 purchase totals = $800.43       $865.1408   $865.14   $865.10   $865.20