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 $182.76   13.796%   $207.9736   $207.97   $207.95   $208.00  
  Purchase #2 $155.57   5.213%   $163.6799   $163.68   $163.70   $163.70  
  Purchase #3 $54.66   4.427%   $57.0798   $57.08   $57.10   $57.10  
  Purchase #4 $25.60   6.790%   $27.3382   $27.34   $27.35   $27.30  
  Purchase #5 $249.93   8.431%   $271.0016   $271.00   $271.00   $271.00  
  Purchase #6 $23.91   9.598%   $26.2049   $26.20   $26.20   $26.20  
  Purchase #7 $106.95   4.563%   $111.8301   $111.83   $111.85   $111.80  
  7 purchase totals = $799.38       $865.1081   $865.10   $865.15   $865.10