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 $228.77   4.748%   $239.632   $239.63   $239.65   $239.60  
  Purchase #2 $116.47   5.310%   $122.6546   $122.65   $122.65   $122.70  
  Purchase #3 $193.32   12.494%   $217.4734   $217.47   $217.45   $217.50  
  Purchase #4 $102.81   9.859%   $112.946   $112.95   $112.95   $112.90  
  Purchase #5 $92.96   12.443%   $104.527   $104.53   $104.55   $104.50  
  Purchase #6 $201.71   3.272%   $208.31   $208.31   $208.30   $208.30  
  Purchase #7 $219.73   10.293%   $242.3468   $242.35   $242.35   $242.30  
  7 purchase totals = $1,155.77       $1,247.8898   $1,247.89   $1,247.90   $1,247.80