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 $244.87   9.542%   $268.2355   $268.24   $268.25   $268.20  
  Purchase #2 $69.32   12.542%   $78.0141   $78.01   $78.00   $78.00  
  Purchase #3 $250.49   4.194%   $260.9956   $261.00   $261.00   $261.00  
  Purchase #4 $67.93   13.646%   $77.1997   $77.20   $77.20   $77.20  
  Purchase #5 $173.81   9.252%   $189.8909   $189.89   $189.90   $189.90  
  Purchase #6 $84.79   9.552%   $92.8891   $92.89   $92.90   $92.90  
  Purchase #7 $58.77   11.492%   $65.5238   $65.52   $65.50   $65.50  
  7 purchase totals = $949.98       $1,032.7487   $1,032.75   $1,032.75   $1,032.70