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 $223.53   13.769%   $254.3078   $254.31   $254.30   $254.30  
  Purchase #2 $94.83   7.856%   $102.2798   $102.28   $102.30   $102.30  
  Purchase #3 $11.44   11.458%   $12.7508   $12.75   $12.75   $12.80  
  Purchase #4 $208.58   7.669%   $224.576   $224.58   $224.60   $224.60  
  Purchase #5 $237.87   13.680%   $270.4106   $270.41   $270.40   $270.40  
  Purchase #6 $163.54   6.538%   $174.2322   $174.23   $174.25   $174.20  
  Purchase #7 $73.37   8.766%   $79.8016   $79.80   $79.80   $79.80  
  7 purchase totals = $1,013.16       $1,118.3588   $1,118.36   $1,118.40   $1,118.40