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 $9.49   3.255%   $9.7989   $9.80   $9.80   $9.80  
  Purchase #2 $156.70   4.514%   $163.7734   $163.77   $163.75   $163.80  
  Purchase #3 $127.92   9.351%   $139.8818   $139.88   $139.90   $139.90  
  Purchase #4 $120.91   7.362%   $129.8114   $129.81   $129.80   $129.80  
  Purchase #5 $60.49   10.425%   $66.7961   $66.80   $66.80   $66.80  
  Purchase #6 $193.42   13.184%   $218.9205   $218.92   $218.90   $218.90  
  Purchase #7 $210.46   8.274%   $227.8735   $227.87   $227.85   $227.90  
  7 purchase totals = $879.39       $956.8556   $956.85   $956.80   $956.90