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 $65.26   13.260%   $73.9135   $73.91   $73.90   $73.90  
  Purchase #2 $181.66   13.330%   $205.8753   $205.88   $205.90   $205.90  
  Purchase #3 $32.93   5.334%   $34.6865   $34.69   $34.70   $34.70  
  Purchase #4 $86.81   6.808%   $92.72   $92.72   $92.70   $92.70  
  Purchase #5 $203.29   8.391%   $220.3481   $220.35   $220.35   $220.30  
  Purchase #6 $114.36   13.406%   $129.6911   $129.69   $129.70   $129.70  
  Purchase #7 $84.45   13.171%   $95.5729   $95.57   $95.55   $95.60  
  7 purchase totals = $768.76       $852.8074   $852.81   $852.80   $852.80