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 $148.46   8.650%   $161.3018   $161.30   $161.30   $161.30  
  Purchase #2 $249.55   13.696%   $283.7284   $283.73   $283.75   $283.70  
  Purchase #3 $88.60   4.807%   $92.859   $92.86   $92.85   $92.90  
  Purchase #4 $246.61   4.493%   $257.6902   $257.69   $257.70   $257.70  
  Purchase #5 $186.89   9.726%   $205.0669   $205.07   $205.05   $205.10  
  Purchase #6 $201.77   3.302%   $208.4324   $208.43   $208.45   $208.40  
  Purchase #7 $124.87   13.383%   $141.5814   $141.58   $141.60   $141.60  
  7 purchase totals = $1,246.75       $1,350.6601   $1,350.66   $1,350.70   $1,350.70