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 $58.48   9.279%   $63.9064   $63.91   $63.90   $63.90  
  Purchase #2 $122.29   11.571%   $136.4402   $136.44   $136.45   $136.40  
  Purchase #3 $86.88   3.225%   $89.6819   $89.68   $89.70   $89.70  
  Purchase #4 $207.94   10.405%   $229.5762   $229.58   $229.60   $229.60  
  Purchase #5 $70.53   4.284%   $73.5515   $73.55   $73.55   $73.60  
  Purchase #6 $96.60   5.652%   $102.0598   $102.06   $102.05   $102.10  
  Purchase #7 $147.78   7.848%   $159.3778   $159.38   $159.40   $159.40  
  7 purchase totals = $790.50       $854.5938   $854.60   $854.65   $854.70