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 $56.62   5.149%   $59.5354   $59.54   $59.55   $59.50  
  Purchase #2 $231.45   12.788%   $261.0478   $261.05   $261.05   $261.00  
  Purchase #3 $80.37   8.395%   $87.1171   $87.12   $87.10   $87.10  
  Purchase #4 $8.93   5.382%   $9.4106   $9.41   $9.40   $9.40  
  Purchase #5 $42.81   13.811%   $48.7225   $48.72   $48.70   $48.70  
  Purchase #6 $58.36   10.264%   $64.3501   $64.35   $64.35   $64.40  
  Purchase #7 $199.70   12.744%   $225.1498   $225.15   $225.15   $225.10  
  7 purchase totals = $678.24       $755.3333   $755.34   $755.30   $755.20