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 $250.36   9.534%   $274.2293   $274.23   $274.25   $274.20  
  Purchase #2 $99.28   5.337%   $104.5786   $104.58   $104.60   $104.60  
  Purchase #3 $105.33   5.482%   $111.1042   $111.10   $111.10   $111.10  
  Purchase #4 $93.36   9.299%   $102.0415   $102.04   $102.05   $102.00  
  Purchase #5 $5.34   4.852%   $5.5991   $5.60   $5.60   $5.60  
  Purchase #6 $69.31   8.120%   $74.938   $74.94   $74.95   $74.90  
  Purchase #7 $231.56   13.411%   $262.6145   $262.61   $262.60   $262.60  
  7 purchase totals = $854.54       $935.1052   $935.10   $935.15   $935.00