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 $46.70   5.652%   $49.3395   $49.34   $49.35   $49.30  
  Purchase #2 $86.39   7.243%   $92.6472   $92.65   $92.65   $92.60  
  Purchase #3 $91.25   8.409%   $98.9232   $98.92   $98.90   $98.90  
  Purchase #4 $106.81   3.439%   $110.4832   $110.48   $110.50   $110.50  
  Purchase #5 $229.59   12.225%   $257.6574   $257.66   $257.65   $257.70  
  Purchase #6 $99.32   3.214%   $102.5121   $102.51   $102.50   $102.50  
  Purchase #7 $202.78   5.259%   $213.4442   $213.44   $213.45   $213.40  
  7 purchase totals = $862.84       $925.0068   $925.00   $925.00   $924.90