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 $86.65   13.377%   $98.2412   $98.24   $98.25   $98.20  
  Purchase #2 $250.46   4.137%   $260.8215   $260.82   $260.80   $260.80  
  Purchase #3 $81.57   8.633%   $88.6119   $88.61   $88.60   $88.60  
  Purchase #4 $8.48   12.770%   $9.5629   $9.56   $9.55   $9.60  
  Purchase #5 $23.69   12.622%   $26.6802   $26.68   $26.70   $26.70  
  Purchase #6 $156.89   12.826%   $177.0127   $177.01   $177.00   $177.00  
  Purchase #7 $226.42   6.771%   $241.7509   $241.75   $241.75   $241.80  
  7 purchase totals = $834.16       $902.6813   $902.67   $902.65   $902.70