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 $63.88   5.576%   $67.4419   $67.44   $67.45   $67.40  
  Purchase #2 $139.28   5.338%   $146.7148   $146.71   $146.70   $146.70  
  Purchase #3 $55.64   11.872%   $62.2456   $62.25   $62.25   $62.20  
  Purchase #4 $240.76   7.562%   $258.9663   $258.97   $258.95   $259.00  
  Purchase #5 $85.37   7.195%   $91.5124   $91.51   $91.50   $91.50  
  Purchase #6 $50.88   8.406%   $55.157   $55.16   $55.15   $55.20  
  Purchase #7 $89.93   4.238%   $93.7412   $93.74   $93.75   $93.70  
  7 purchase totals = $725.74       $775.7792   $775.78   $775.75   $775.70