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 $86.46   13.458%   $98.0958   $98.10   $98.10   $98.10  
  Purchase #2 $121.38   6.226%   $128.9371   $128.94   $128.95   $128.90  
  Purchase #3 $194.67   5.619%   $205.6085   $205.61   $205.60   $205.60  
  Purchase #4 $201.39   11.289%   $224.1249   $224.12   $224.10   $224.10  
  Purchase #5 $127.91   13.719%   $145.458   $145.46   $145.45   $145.50  
  Purchase #6 $148.41   3.686%   $153.8804   $153.88   $153.90   $153.90  
  Purchase #7 $68.41   13.697%   $77.7801   $77.78   $77.80   $77.80  
  7 purchase totals = $948.63       $1,033.8848   $1,033.89   $1,033.90   $1,033.90