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 $232.67   12.218%   $261.0976   $261.10   $261.10   $261.10  
  Purchase #2 $228.93   13.210%   $259.1717   $259.17   $259.15   $259.20  
  Purchase #3 $111.66   5.216%   $117.4842   $117.48   $117.50   $117.50  
  Purchase #4 $165.52   9.124%   $180.622   $180.62   $180.60   $180.60  
  Purchase #5 $61.70   11.525%   $68.8109   $68.81   $68.80   $68.80  
  Purchase #6 $111.29   11.187%   $123.74   $123.74   $123.75   $123.70  
  Purchase #7 $190.72   3.470%   $197.338   $197.34   $197.35   $197.30  
  7 purchase totals = $1,102.49       $1,208.2644   $1,208.26   $1,208.25   $1,208.20