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 $197.37   5.709%   $208.6379   $208.64   $208.65   $208.60  
  Purchase #2 $11.82   12.133%   $13.2541   $13.25   $13.25   $13.30  
  Purchase #3 $109.59   8.690%   $119.1134   $119.11   $119.10   $119.10  
  Purchase #4 $235.73   10.818%   $261.2313   $261.23   $261.25   $261.20  
  Purchase #5 $55.52   9.825%   $60.9748   $60.97   $60.95   $61.00  
  Purchase #6 $167.83   5.418%   $176.923   $176.92   $176.90   $176.90  
  Purchase #7 $200.65   13.534%   $227.806   $227.81   $227.80   $227.80  
  7 purchase totals = $978.51       $1,067.9405   $1,067.93   $1,067.90   $1,067.90