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 $24.49   9.317%   $26.7717   $26.77   $26.75   $26.80  
  Purchase #2 $173.58   10.120%   $191.1463   $191.15   $191.15   $191.10  
  Purchase #3 $199.57   4.201%   $207.9539   $207.95   $207.95   $208.00  
  Purchase #4 $96.45   5.762%   $102.0074   $102.01   $102.00   $102.00  
  Purchase #5 $30.97   9.797%   $34.0041   $34.00   $34.00   $34.00  
  Purchase #6 $247.57   3.161%   $255.3957   $255.40   $255.40   $255.40  
  Purchase #7 $118.49   7.764%   $127.6896   $127.69   $127.70   $127.70  
  7 purchase totals = $891.12       $944.9687   $944.97   $944.95   $945.00