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 $58.95   10.849%   $65.3455   $65.35   $65.35   $65.30  
  Purchase #2 $40.64   4.569%   $42.4968   $42.50   $42.50   $42.50  
  Purchase #3 $44.90   13.322%   $50.8816   $50.88   $50.90   $50.90  
  Purchase #4 $225.25   12.266%   $252.8792   $252.88   $252.90   $252.90  
  Purchase #5 $73.72   3.841%   $76.5516   $76.55   $76.55   $76.60  
  Purchase #6 $191.65   5.505%   $202.2003   $202.20   $202.20   $202.20  
  Purchase #7 $57.50   12.109%   $64.4627   $64.46   $64.45   $64.50  
  7 purchase totals = $692.61       $754.8177   $754.82   $754.85   $754.90