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 $24.28   8.202%   $26.2714   $26.27   $26.25   $26.30  
  Purchase #2 $153.48   13.824%   $174.6971   $174.70   $174.70   $174.70  
  Purchase #3 $148.65   10.489%   $164.2419   $164.24   $164.25   $164.20  
  Purchase #4 $79.44   4.210%   $82.7844   $82.78   $82.80   $82.80  
  Purchase #5 $186.84   11.162%   $207.6951   $207.70   $207.70   $207.70  
  Purchase #6 $58.28   8.603%   $63.2938   $63.29   $63.30   $63.30  
  Purchase #7 $47.96   11.738%   $53.5895   $53.59   $53.60   $53.60  
  7 purchase totals = $698.93       $772.5732   $772.57   $772.60   $772.60