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 $57.51   11.778%   $64.2835   $64.28   $64.30   $64.30  
  Purchase #2 $236.66   12.427%   $266.0697   $266.07   $266.05   $266.10  
  Purchase #3 $112.68   7.429%   $121.051   $121.05   $121.05   $121.10  
  Purchase #4 $181.28   8.479%   $196.6507   $196.65   $196.65   $196.70  
  Purchase #5 $244.84   6.858%   $261.6311   $261.63   $261.65   $261.60  
  Purchase #6 $146.52   13.256%   $165.9427   $165.94   $165.95   $165.90  
  Purchase #7 $5.76   10.782%   $6.381   $6.38   $6.40   $6.40  
  7 purchase totals = $985.25       $1,082.0097   $1,082.00   $1,082.05   $1,082.10