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 $63.58   8.551%   $69.0167   $69.02   $69.00   $69.00  
  Purchase #2 $213.85   5.184%   $224.936   $224.94   $224.95   $224.90  
  Purchase #3 $49.66   7.358%   $53.314   $53.31   $53.30   $53.30  
  Purchase #4 $221.35   7.335%   $237.586   $237.59   $237.60   $237.60  
  Purchase #5 $27.87   4.305%   $29.0698   $29.07   $29.05   $29.10  
  Purchase #6 $172.94   6.330%   $183.8871   $183.89   $183.90   $183.90  
  Purchase #7 $6.39   13.223%   $7.2349   $7.23   $7.25   $7.20  
  7 purchase totals = $755.64       $805.0445   $805.05   $805.05   $805.00