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 $141.63   13.484%   $160.7274   $160.73   $160.75   $160.70  
  Purchase #2 $176.77   12.588%   $199.0218   $199.02   $199.00   $199.00  
  Purchase #3 $101.88   3.205%   $105.1453   $105.15   $105.15   $105.10  
  Purchase #4 $203.37   13.396%   $230.6134   $230.61   $230.60   $230.60  
  Purchase #5 $227.53   9.244%   $248.5629   $248.56   $248.55   $248.60  
  Purchase #6 $23.40   12.273%   $26.2719   $26.27   $26.25   $26.30  
  Purchase #7 $50.31   10.806%   $55.7465   $55.75   $55.75   $55.70  
  7 purchase totals = $924.89       $1,026.0892   $1,026.09   $1,026.05   $1,026.00