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 $56.81   3.862%   $59.004   $59.00   $59.00   $59.00  
  Purchase #2 $159.60   3.386%   $165.0041   $165.00   $165.00   $165.00  
  Purchase #3 $7.51   12.396%   $8.4409   $8.44   $8.45   $8.40  
  Purchase #4 $233.83   11.638%   $261.0431   $261.04   $261.05   $261.00  
  Purchase #5 $56.94   12.765%   $64.2084   $64.21   $64.20   $64.20  
  Purchase #6 $139.25   5.477%   $146.8767   $146.88   $146.90   $146.90  
  Purchase #7 $71.63   8.310%   $77.5825   $77.58   $77.60   $77.60  
  7 purchase totals = $725.57       $782.1597   $782.15   $782.20   $782.10