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 $120.35   4.239%   $125.4516   $125.45   $125.45   $125.50  
  Purchase #2 $248.37   4.423%   $259.3554   $259.36   $259.35   $259.40  
  Purchase #3 $216.56   4.238%   $225.7378   $225.74   $225.75   $225.70  
  Purchase #4 $237.44   5.805%   $251.2234   $251.22   $251.20   $251.20  
  Purchase #5 $187.51   9.732%   $205.7585   $205.76   $205.75   $205.80  
  Purchase #6 $125.64   4.103%   $130.795   $130.80   $130.80   $130.80  
  Purchase #7 $27.29   11.345%   $30.3861   $30.39   $30.40   $30.40  
  7 purchase totals = $1,163.16       $1,228.7078   $1,228.72   $1,228.70   $1,228.80