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 $38.75   7.260%   $41.5633   $41.56   $41.55   $41.60  
  Purchase #2 $214.30   10.536%   $236.8786   $236.88   $236.90   $236.90  
  Purchase #3 $104.83   8.574%   $113.8181   $113.82   $113.80   $113.80  
  Purchase #4 $12.64   13.219%   $14.3109   $14.31   $14.30   $14.30  
  Purchase #5 $125.63   3.427%   $129.9353   $129.94   $129.95   $129.90  
  Purchase #6 $248.81   5.629%   $262.8155   $262.82   $262.80   $262.80  
  Purchase #7 $121.37   11.827%   $135.7244   $135.72   $135.70   $135.70  
  7 purchase totals = $866.33       $935.0461   $935.05   $935.00   $935.00