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 $56.70   12.302%   $63.6752   $63.68   $63.70   $63.70  
  Purchase #2 $44.93   4.263%   $46.8454   $46.85   $46.85   $46.80  
  Purchase #3 $192.97   9.187%   $210.6982   $210.70   $210.70   $210.70  
  Purchase #4 $248.72   5.299%   $261.8997   $261.90   $261.90   $261.90  
  Purchase #5 $111.49   7.598%   $119.961   $119.96   $119.95   $120.00  
  Purchase #6 $33.91   13.268%   $38.4092   $38.41   $38.40   $38.40  
  Purchase #7 $182.97   10.229%   $201.686   $201.69   $201.70   $201.70  
  7 purchase totals = $871.69       $943.1747   $943.19   $943.20   $943.20