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 $118.63   13.493%   $134.6367   $134.64   $134.65   $134.60  
  Purchase #2 $176.25   12.559%   $198.3852   $198.39   $198.40   $198.40  
  Purchase #3 $54.73   11.624%   $61.0918   $61.09   $61.10   $61.10  
  Purchase #4 $69.40   13.662%   $78.8814   $78.88   $78.90   $78.90  
  Purchase #5 $76.27   12.582%   $85.8663   $85.87   $85.85   $85.90  
  Purchase #6 $175.61   10.649%   $194.3107   $194.31   $194.30   $194.30  
  Purchase #7 $205.90   12.788%   $232.2305   $232.23   $232.25   $232.20  
  7 purchase totals = $876.79       $985.4026   $985.41   $985.45   $985.40