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 $176.97   13.837%   $201.4573   $201.46   $201.45   $201.50  
  Purchase #2 $114.95   6.835%   $122.8068   $122.81   $122.80   $122.80  
  Purchase #3 $42.69   8.547%   $46.3387   $46.34   $46.35   $46.30  
  Purchase #4 $174.73   7.769%   $188.3048   $188.30   $188.30   $188.30  
  Purchase #5 $125.42   10.154%   $138.1551   $138.16   $138.15   $138.20  
  Purchase #6 $234.59   8.169%   $253.7537   $253.75   $253.75   $253.80  
  Purchase #7 $225.77   10.798%   $250.1486   $250.15   $250.15   $250.10  
  7 purchase totals = $1,095.12       $1,200.9650   $1,200.97   $1,200.95   $1,201.00