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 $209.36   11.444%   $233.3192   $233.32   $233.30   $233.30  
  Purchase #2 $25.62   4.207%   $26.6978   $26.70   $26.70   $26.70  
  Purchase #3 $59.53   12.866%   $67.1891   $67.19   $67.20   $67.20  
  Purchase #4 $35.62   8.299%   $38.5761   $38.58   $38.60   $38.60  
  Purchase #5 $209.67   8.398%   $227.2781   $227.28   $227.30   $227.30  
  Purchase #6 $76.32   13.352%   $86.5102   $86.51   $86.50   $86.50  
  Purchase #7 $212.58   11.280%   $236.559   $236.56   $236.55   $236.60  
  7 purchase totals = $828.70       $916.1295   $916.14   $916.15   $916.20