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 $213.54   13.406%   $242.1672   $242.17   $242.15   $242.20  
  Purchase #2 $231.79   12.834%   $261.5379   $261.54   $261.55   $261.50  
  Purchase #3 $225.71   8.340%   $244.5342   $244.53   $244.55   $244.50  
  Purchase #4 $23.59   4.796%   $24.7214   $24.72   $24.70   $24.70  
  Purchase #5 $225.70   12.212%   $253.2625   $253.26   $253.25   $253.30  
  Purchase #6 $155.28   5.257%   $163.4431   $163.44   $163.45   $163.40  
  Purchase #7 $57.91   4.168%   $60.3237   $60.32   $60.30   $60.30  
  7 purchase totals = $1,133.52       $1,249.9900   $1,249.98   $1,249.95   $1,249.90