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 $245.25   6.441%   $261.0466   $261.05   $261.05   $261.00  
  Purchase #2 $113.90   11.143%   $126.5919   $126.59   $126.60   $126.60  
  Purchase #3 $239.28   12.355%   $268.843   $268.84   $268.85   $268.80  
  Purchase #4 $145.25   12.315%   $163.1375   $163.14   $163.15   $163.10  
  Purchase #5 $184.69   4.577%   $193.1433   $193.14   $193.15   $193.10  
  Purchase #6 $126.42   11.524%   $140.9886   $140.99   $141.00   $141.00  
  Purchase #7 $180.73   6.798%   $193.016   $193.02   $193.00   $193.00  
  7 purchase totals = $1,235.52       $1,346.7669   $1,346.77   $1,346.80   $1,346.60