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 $96.60   5.284%   $101.7043   $101.70   $101.70   $101.70  
  Purchase #2 $238.84   8.666%   $259.5379   $259.54   $259.55   $259.50  
  Purchase #3 $64.54   8.308%   $69.902   $69.90   $69.90   $69.90  
  Purchase #4 $160.93   13.598%   $182.8133   $182.81   $182.80   $182.80  
  Purchase #5 $158.89   11.474%   $177.121   $177.12   $177.10   $177.10  
  Purchase #6 $6.71   6.233%   $7.1282   $7.13   $7.15   $7.10  
  Purchase #7 $104.91   9.443%   $114.8167   $114.82   $114.80   $114.80  
  7 purchase totals = $831.42       $913.0234   $913.02   $913.00   $912.90