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 $160.70   10.238%   $177.1525   $177.15   $177.15   $177.20  
  Purchase #2 $69.92   12.455%   $78.6285   $78.63   $78.65   $78.60  
  Purchase #3 $26.76   8.345%   $28.9931   $28.99   $29.00   $29.00  
  Purchase #4 $212.32   11.812%   $237.3992   $237.40   $237.40   $237.40  
  Purchase #5 $118.61   4.537%   $123.9913   $123.99   $124.00   $124.00  
  Purchase #6 $240.59   8.150%   $260.1981   $260.20   $260.20   $260.20  
  Purchase #7 $26.81   9.187%   $29.273   $29.27   $29.25   $29.30  
  7 purchase totals = $855.71       $935.6357   $935.63   $935.65   $935.70