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 $227.41   11.202%   $252.8845   $252.88   $252.90   $252.90  
  Purchase #2 $115.77   5.624%   $122.2809   $122.28   $122.30   $122.30  
  Purchase #3 $156.45   7.302%   $167.874   $167.87   $167.85   $167.90  
  Purchase #4 $205.58   13.223%   $232.7638   $232.76   $232.75   $232.80  
  Purchase #5 $54.82   8.213%   $59.3224   $59.32   $59.30   $59.30  
  Purchase #6 $106.32   3.760%   $110.3176   $110.32   $110.30   $110.30  
  Purchase #7 $240.28   8.635%   $261.0282   $261.03   $261.05   $261.00  
  7 purchase totals = $1,106.63       $1,206.4714   $1,206.46   $1,206.45   $1,206.50