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 $208.38   12.753%   $234.9547   $234.95   $234.95   $235.00  
  Purchase #2 $23.75   8.208%   $25.6994   $25.70   $25.70   $25.70  
  Purchase #3 $125.68   13.688%   $142.8831   $142.88   $142.90   $142.90  
  Purchase #4 $134.81   6.314%   $143.3219   $143.32   $143.30   $143.30  
  Purchase #5 $80.41   3.472%   $83.2018   $83.20   $83.20   $83.20  
  Purchase #6 $9.92   3.860%   $10.3029   $10.30   $10.30   $10.30  
  Purchase #7 $182.71   5.360%   $192.5033   $192.50   $192.50   $192.50  
  7 purchase totals = $765.66       $832.8671   $832.85   $832.85   $832.90