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 $155.26   7.582%   $167.0318   $167.03   $167.05   $167.00  
  Purchase #2 $239.69   3.797%   $248.791   $248.79   $248.80   $248.80  
  Purchase #3 $18.32   7.337%   $19.6641   $19.66   $19.65   $19.70  
  Purchase #4 $186.63   8.691%   $202.85   $202.85   $202.85   $202.90  
  Purchase #5 $179.66   13.828%   $204.5034   $204.50   $204.50   $204.50  
  Purchase #6 $199.81   7.408%   $214.6119   $214.61   $214.60   $214.60  
  Purchase #7 $199.37   3.351%   $206.0509   $206.05   $206.05   $206.10  
  7 purchase totals = $1,178.74       $1,263.5031   $1,263.49   $1,263.50   $1,263.60