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 $201.54   12.518%   $226.7688   $226.77   $226.75   $226.80  
  Purchase #2 $109.71   11.685%   $122.5296   $122.53   $122.55   $122.50  
  Purchase #3 $164.98   6.161%   $175.1444   $175.14   $175.15   $175.10  
  Purchase #4 $105.74   12.723%   $119.1933   $119.19   $119.20   $119.20  
  Purchase #5 $146.77   4.674%   $153.63   $153.63   $153.65   $153.60  
  Purchase #6 $196.81   12.137%   $220.6968   $220.70   $220.70   $220.70  
  Purchase #7 $208.93   4.408%   $218.1396   $218.14   $218.15   $218.10  
  7 purchase totals = $1,134.48       $1,236.1025   $1,236.10   $1,236.15   $1,236.00