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 $228.33   13.721%   $259.6592   $259.66   $259.65   $259.70  
  Purchase #2 $153.77   5.710%   $162.5503   $162.55   $162.55   $162.60  
  Purchase #3 $195.28   5.836%   $206.6765   $206.68   $206.70   $206.70  
  Purchase #4 $32.85   9.588%   $35.9997   $36.00   $36.00   $36.00  
  Purchase #5 $140.36   4.674%   $146.9204   $146.92   $146.90   $146.90  
  Purchase #6 $35.79   10.136%   $39.4177   $39.42   $39.40   $39.40  
  Purchase #7 $41.30   8.219%   $44.6944   $44.69   $44.70   $44.70  
  7 purchase totals = $827.68       $895.9182   $895.92   $895.90   $896.00