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 $59.49   8.613%   $64.6139   $64.61   $64.60   $64.60  
  Purchase #2 $127.46   7.305%   $136.771   $136.77   $136.75   $136.80  
  Purchase #3 $199.27   9.381%   $217.9635   $217.96   $217.95   $218.00  
  Purchase #4 $227.68   4.386%   $237.666   $237.67   $237.65   $237.70  
  Purchase #5 $50.82   13.322%   $57.5902   $57.59   $57.60   $57.60  
  Purchase #6 $133.60   5.706%   $141.2232   $141.22   $141.20   $141.20  
  Purchase #7 $131.65   5.558%   $138.9671   $138.97   $138.95   $139.00  
  7 purchase totals = $929.97       $994.7949   $994.79   $994.70   $994.90