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 $236.74   10.478%   $261.5456   $261.55   $261.55   $261.50  
  Purchase #2 $57.25   8.124%   $61.901   $61.90   $61.90   $61.90  
  Purchase #3 $52.81   4.460%   $55.1653   $55.17   $55.15   $55.20  
  Purchase #4 $70.46   8.405%   $76.3822   $76.38   $76.40   $76.40  
  Purchase #5 $223.45   6.245%   $237.4045   $237.40   $237.40   $237.40  
  Purchase #6 $21.27   13.446%   $24.13   $24.13   $24.15   $24.10  
  Purchase #7 $193.78   11.626%   $216.3089   $216.31   $216.30   $216.30  
  7 purchase totals = $855.76       $932.8375   $932.84   $932.85   $932.80