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 $206.68   11.121%   $229.6649   $229.66   $229.65   $229.70  
  Purchase #2 $215.91   3.856%   $224.2355   $224.24   $224.25   $224.20  
  Purchase #3 $17.89   3.115%   $18.4473   $18.45   $18.45   $18.40  
  Purchase #4 $146.31   12.798%   $165.0348   $165.03   $165.05   $165.00  
  Purchase #5 $155.99   13.823%   $177.5525   $177.55   $177.55   $177.60  
  Purchase #6 $196.59   9.874%   $216.0013   $216.00   $216.00   $216.00  
  Purchase #7 $125.90   3.466%   $130.2637   $130.26   $130.25   $130.30  
  7 purchase totals = $1,065.27       $1,161.2000   $1,161.19   $1,161.20   $1,161.20