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 $240.67   8.541%   $261.2256   $261.23   $261.25   $261.20  
  Purchase #2 $98.72   11.435%   $110.0086   $110.01   $110.00   $110.00  
  Purchase #3 $133.94   7.638%   $144.1703   $144.17   $144.15   $144.20  
  Purchase #4 $163.25   13.619%   $185.483   $185.48   $185.50   $185.50  
  Purchase #5 $76.86   11.437%   $85.6505   $85.65   $85.65   $85.70  
  Purchase #6 $56.92   7.623%   $61.259   $61.26   $61.25   $61.30  
  Purchase #7 $115.62   5.488%   $121.9652   $121.97   $121.95   $122.00  
  7 purchase totals = $885.98       $969.7622   $969.77   $969.75   $969.90