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 $114.67   4.246%   $119.5389   $119.54   $119.55   $119.50  
  Purchase #2 $195.63   6.445%   $208.2384   $208.24   $208.25   $208.20  
  Purchase #3 $217.30   8.459%   $235.6814   $235.68   $235.70   $235.70  
  Purchase #4 $16.42   3.605%   $17.0119   $17.01   $17.00   $17.00  
  Purchase #5 $195.42   5.126%   $205.4372   $205.44   $205.45   $205.40  
  Purchase #6 $77.86   3.632%   $80.6879   $80.69   $80.70   $80.70  
  Purchase #7 $68.41   5.290%   $72.0289   $72.03   $72.05   $72.00  
  7 purchase totals = $885.71       $938.6246   $938.63   $938.70   $938.50