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 $81.86   13.443%   $92.8644   $92.86   $92.85   $92.90  
  Purchase #2 $239.46   10.596%   $264.8332   $264.83   $264.85   $264.80  
  Purchase #3 $146.69   13.641%   $166.7   $166.70   $166.70   $166.70  
  Purchase #4 $13.41   11.494%   $14.9513   $14.95   $14.95   $15.00  
  Purchase #5 $174.95   6.765%   $186.7854   $186.79   $186.80   $186.80  
  Purchase #6 $11.67   4.798%   $12.2299   $12.23   $12.25   $12.20  
  Purchase #7 $104.50   7.368%   $112.1996   $112.20   $112.20   $112.20  
  7 purchase totals = $772.54       $850.5638   $850.56   $850.60   $850.60