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 $196.49   5.448%   $207.1948   $207.19   $207.20   $207.20  
  Purchase #2 $82.59   9.257%   $90.2354   $90.24   $90.25   $90.20  
  Purchase #3 $118.85   4.616%   $124.3361   $124.34   $124.35   $124.30  
  Purchase #4 $58.26   11.576%   $65.0042   $65.00   $65.00   $65.00  
  Purchase #5 $147.97   5.838%   $156.6085   $156.61   $156.60   $156.60  
  Purchase #6 $162.36   10.854%   $179.9826   $179.98   $180.00   $180.00  
  Purchase #7 $27.36   12.185%   $30.6938   $30.69   $30.70   $30.70  
  7 purchase totals = $793.88       $854.0554   $854.05   $854.10   $854.00