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 $79.41   3.259%   $81.998   $82.00   $82.00   $82.00  
  Purchase #2 $114.70   9.464%   $125.5552   $125.56   $125.55   $125.60  
  Purchase #3 $62.42   4.160%   $65.0167   $65.02   $65.00   $65.00  
  Purchase #4 $143.26   6.527%   $152.6106   $152.61   $152.60   $152.60  
  Purchase #5 $118.49   6.212%   $125.8506   $125.85   $125.85   $125.90  
  Purchase #6 $86.67   10.689%   $95.9342   $95.93   $95.95   $95.90  
  Purchase #7 $71.50   3.484%   $73.9911   $73.99   $74.00   $74.00  
  7 purchase totals = $676.45       $720.9564   $720.96   $720.95   $721.00