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 $23.61   6.587%   $25.1652   $25.17   $25.15   $25.20  
  Purchase #2 $176.56   13.682%   $200.7169   $200.72   $200.70   $200.70  
  Purchase #3 $103.93   7.472%   $111.6956   $111.70   $111.70   $111.70  
  Purchase #4 $192.75   7.635%   $207.4665   $207.47   $207.45   $207.50  
  Purchase #5 $126.80   8.254%   $137.2661   $137.27   $137.25   $137.30  
  Purchase #6 $162.91   5.387%   $171.686   $171.69   $171.70   $171.70  
  Purchase #7 $122.28   9.544%   $133.9504   $133.95   $133.95   $134.00  
  7 purchase totals = $908.84       $987.9467   $987.97   $987.90   $988.10