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 $57.66   5.614%   $60.897   $60.90   $60.90   $60.90  
  Purchase #2 $126.71   13.539%   $143.8653   $143.87   $143.85   $143.90  
  Purchase #3 $157.66   6.848%   $168.4566   $168.46   $168.45   $168.50  
  Purchase #4 $206.92   5.189%   $217.6571   $217.66   $217.65   $217.70  
  Purchase #5 $79.80   11.181%   $88.7224   $88.72   $88.70   $88.70  
  Purchase #6 $197.57   11.819%   $220.9208   $220.92   $220.90   $220.90  
  Purchase #7 $208.97   3.228%   $215.7156   $215.72   $215.70   $215.70  
  7 purchase totals = $1,035.29       $1,116.2348   $1,116.25   $1,116.15   $1,116.30