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 $124.41   7.794%   $134.1065   $134.11   $134.10   $134.10  
  Purchase #2 $216.60   13.774%   $246.4345   $246.43   $246.45   $246.40  
  Purchase #3 $47.48   13.452%   $53.867   $53.87   $53.85   $53.90  
  Purchase #4 $57.69   6.737%   $61.5766   $61.58   $61.60   $61.60  
  Purchase #5 $74.83   11.495%   $83.4317   $83.43   $83.45   $83.40  
  Purchase #6 $142.44   3.718%   $147.7359   $147.74   $147.75   $147.70  
  Purchase #7 $122.72   11.404%   $136.715   $136.72   $136.70   $136.70  
  7 purchase totals = $786.17       $863.8672   $863.88   $863.90   $863.80