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 $117.25   5.697%   $123.9297   $123.93   $123.95   $123.90  
  Purchase #2 $90.72   7.474%   $97.5004   $97.50   $97.50   $97.50  
  Purchase #3 $184.90   12.868%   $208.6929   $208.69   $208.70   $208.70  
  Purchase #4 $84.88   6.725%   $90.5882   $90.59   $90.60   $90.60  
  Purchase #5 $185.68   6.143%   $197.0863   $197.09   $197.10   $197.10  
  Purchase #6 $77.33   11.345%   $86.1031   $86.10   $86.10   $86.10  
  Purchase #7 $227.75   12.597%   $256.4397   $256.44   $256.45   $256.40  
  7 purchase totals = $968.51       $1,060.3403   $1,060.34   $1,060.40   $1,060.30