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 $71.82   5.712%   $75.9224   $75.92   $75.90   $75.90  
  Purchase #2 $71.96   6.571%   $76.6885   $76.69   $76.70   $76.70  
  Purchase #3 $127.58   12.351%   $143.3374   $143.34   $143.35   $143.30  
  Purchase #4 $177.90   9.651%   $195.0691   $195.07   $195.05   $195.10  
  Purchase #5 $8.37   4.189%   $8.7206   $8.72   $8.70   $8.70  
  Purchase #6 $179.85   7.638%   $193.5869   $193.59   $193.60   $193.60  
  Purchase #7 $44.91   3.321%   $46.4015   $46.40   $46.40   $46.40  
  7 purchase totals = $682.39       $739.7264   $739.73   $739.70   $739.70