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 $209.34   12.503%   $235.5138   $235.51   $235.50   $235.50  
  Purchase #2 $10.55   6.273%   $11.2118   $11.21   $11.20   $11.20  
  Purchase #3 $217.69   4.388%   $227.2422   $227.24   $227.25   $227.20  
  Purchase #4 $200.34   10.838%   $222.0528   $222.05   $222.05   $222.10  
  Purchase #5 $199.59   4.532%   $208.6354   $208.64   $208.65   $208.60  
  Purchase #6 $67.45   8.866%   $73.4301   $73.43   $73.45   $73.40  
  Purchase #7 $156.97   4.178%   $163.5282   $163.53   $163.55   $163.50  
  7 purchase totals = $1,061.93       $1,141.6143   $1,141.61   $1,141.65   $1,141.50