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 $241.54   8.757%   $262.6917   $262.69   $262.70   $262.70  
  Purchase #2 $80.88   4.291%   $84.3506   $84.35   $84.35   $84.40  
  Purchase #3 $64.33   7.735%   $69.3059   $69.31   $69.30   $69.30  
  Purchase #4 $119.54   5.385%   $125.9772   $125.98   $126.00   $126.00  
  Purchase #5 $157.86   7.365%   $169.4864   $169.49   $169.50   $169.50  
  Purchase #6 $44.43   3.858%   $46.1441   $46.14   $46.15   $46.10  
  Purchase #7 $128.92   7.843%   $139.0312   $139.03   $139.05   $139.00  
  7 purchase totals = $837.50       $896.9871   $896.99   $897.05   $897.00