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 $60.94   4.631%   $63.7621   $63.76   $63.75   $63.80  
  Purchase #2 $53.30   8.303%   $57.7255   $57.73   $57.75   $57.70  
  Purchase #3 $235.31   6.425%   $250.4287   $250.43   $250.45   $250.40  
  Purchase #4 $132.81   7.688%   $143.0204   $143.02   $143.00   $143.00  
  Purchase #5 $171.77   4.139%   $178.8796   $178.88   $178.90   $178.90  
  Purchase #6 $106.61   4.807%   $111.7347   $111.73   $111.75   $111.70  
  Purchase #7 $227.31   3.692%   $235.7023   $235.70   $235.70   $235.70  
  7 purchase totals = $988.05       $1,041.2533   $1,041.25   $1,041.30   $1,041.20