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 $25.46   3.853%   $26.441   $26.44   $26.45   $26.40  
  Purchase #2 $163.58   9.656%   $179.3753   $179.38   $179.40   $179.40  
  Purchase #3 $88.42   4.728%   $92.6005   $92.60   $92.60   $92.60  
  Purchase #4 $135.86   3.704%   $140.8923   $140.89   $140.90   $140.90  
  Purchase #5 $215.99   7.210%   $231.5629   $231.56   $231.55   $231.60  
  Purchase #6 $193.53   11.332%   $215.4608   $215.46   $215.45   $215.50  
  Purchase #7 $169.46   11.693%   $189.275   $189.28   $189.30   $189.30  
  7 purchase totals = $992.30       $1,075.6078   $1,075.61   $1,075.65   $1,075.70