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 $115.48   7.517%   $124.1606   $124.16   $124.15   $124.20  
  Purchase #2 $124.69   4.864%   $130.7549   $130.75   $130.75   $130.80  
  Purchase #3 $32.53   3.569%   $33.691   $33.69   $33.70   $33.70  
  Purchase #4 $39.70   4.861%   $41.6298   $41.63   $41.65   $41.60  
  Purchase #5 $241.61   6.644%   $257.6626   $257.66   $257.65   $257.70  
  Purchase #6 $146.87   11.279%   $163.4355   $163.44   $163.45   $163.40  
  Purchase #7 $243.32   6.603%   $259.3864   $259.39   $259.40   $259.40  
  7 purchase totals = $944.20       $1,010.7208   $1,010.72   $1,010.75   $1,010.80