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 $125.96   12.867%   $142.1673   $142.17   $142.15   $142.20  
  Purchase #2 $93.98   10.558%   $103.9024   $103.90   $103.90   $103.90  
  Purchase #3 $151.47   8.639%   $164.5555   $164.56   $164.55   $164.60  
  Purchase #4 $196.42   3.103%   $202.5149   $202.51   $202.50   $202.50  
  Purchase #5 $163.25   6.128%   $173.254   $173.25   $173.25   $173.30  
  Purchase #6 $175.77   8.426%   $190.5804   $190.58   $190.60   $190.60  
  Purchase #7 $6.95   3.184%   $7.1713   $7.17   $7.15   $7.20  
  7 purchase totals = $913.80       $984.1458   $984.14   $984.10   $984.30