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 $153.53   7.197%   $164.5796   $164.58   $164.60   $164.60  
  Purchase #2 $62.64   3.851%   $65.0523   $65.05   $65.05   $65.10  
  Purchase #3 $225.94   9.783%   $248.0437   $248.04   $248.05   $248.00  
  Purchase #4 $188.60   6.240%   $200.3686   $200.37   $200.35   $200.40  
  Purchase #5 $248.83   12.693%   $280.414   $280.41   $280.40   $280.40  
  Purchase #6 $157.92   3.587%   $163.5846   $163.58   $163.60   $163.60  
  Purchase #7 $69.54   4.219%   $72.4739   $72.47   $72.45   $72.50  
  7 purchase totals = $1,107.00       $1,194.5167   $1,194.50   $1,194.50   $1,194.60