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 $10.93   6.408%   $11.6304   $11.63   $11.65   $11.60  
  Purchase #2 $177.93   13.475%   $201.9061   $201.91   $201.90   $201.90  
  Purchase #3 $168.50   11.201%   $187.3737   $187.37   $187.35   $187.40  
  Purchase #4 $133.76   5.598%   $141.2479   $141.25   $141.25   $141.20  
  Purchase #5 $74.77   12.870%   $84.3929   $84.39   $84.40   $84.40  
  Purchase #6 $101.86   12.386%   $114.4764   $114.48   $114.50   $114.50  
  Purchase #7 $90.81   13.199%   $102.796   $102.80   $102.80   $102.80  
  7 purchase totals = $758.56       $843.8234   $843.83   $843.85   $843.80