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 $183.38   13.796%   $208.6791   $208.68   $208.70   $208.70  
  Purchase #2 $235.44   4.501%   $246.0372   $246.04   $246.05   $246.00  
  Purchase #3 $195.79   7.834%   $211.1282   $211.13   $211.15   $211.10  
  Purchase #4 $157.38   12.218%   $176.6087   $176.61   $176.60   $176.60  
  Purchase #5 $216.58   6.474%   $230.6014   $230.60   $230.60   $230.60  
  Purchase #6 $58.26   12.750%   $65.6882   $65.69   $65.70   $65.70  
  Purchase #7 $177.42   13.289%   $200.9973   $201.00   $201.00   $201.00  
  7 purchase totals = $1,224.25       $1,339.7401   $1,339.75   $1,339.80   $1,339.70