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 $86.62   13.630%   $98.4263   $98.43   $98.45   $98.40  
  Purchase #2 $162.89   6.783%   $173.9388   $173.94   $173.95   $173.90  
  Purchase #3 $154.82   6.322%   $164.6077   $164.61   $164.60   $164.60  
  Purchase #4 $26.64   13.617%   $30.2676   $30.27   $30.25   $30.30  
  Purchase #5 $18.88   4.629%   $19.754   $19.75   $19.75   $19.80  
  Purchase #6 $220.97   12.642%   $248.905   $248.91   $248.90   $248.90  
  Purchase #7 $199.43   4.774%   $208.9508   $208.95   $208.95   $209.00  
  7 purchase totals = $870.25       $944.8502   $944.86   $944.85   $944.90