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 $49.88   3.407%   $51.5794   $51.58   $51.60   $51.60  
  Purchase #2 $119.26   5.860%   $126.2486   $126.25   $126.25   $126.20  
  Purchase #3 $229.92   13.535%   $261.0397   $261.04   $261.05   $261.00  
  Purchase #4 $167.90   10.610%   $185.7142   $185.71   $185.70   $185.70  
  Purchase #5 $109.57   13.164%   $123.9938   $123.99   $124.00   $124.00  
  Purchase #6 $154.83   3.446%   $160.1654   $160.17   $160.15   $160.20  
  Purchase #7 $147.42   13.625%   $167.506   $167.51   $167.50   $167.50  
  7 purchase totals = $978.78       $1,076.2471   $1,076.25   $1,076.25   $1,076.20