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 $240.41   8.508%   $260.8641   $260.86   $260.85   $260.90  
  Purchase #2 $23.97   6.724%   $25.5817   $25.58   $25.60   $25.60  
  Purchase #3 $240.73   7.729%   $259.336   $259.34   $259.35   $259.30  
  Purchase #4 $56.57   11.719%   $63.1994   $63.20   $63.20   $63.20  
  Purchase #5 $119.48   10.220%   $131.6909   $131.69   $131.70   $131.70  
  Purchase #6 $105.39   12.421%   $118.4805   $118.48   $118.50   $118.50  
  Purchase #7 $232.99   9.726%   $255.6506   $255.65   $255.65   $255.70  
  7 purchase totals = $1,019.54       $1,114.8032   $1,114.80   $1,114.85   $1,114.90