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 $248.93   7.602%   $267.8537   $267.85   $267.85   $267.90  
  Purchase #2 $122.84   10.783%   $136.0858   $136.09   $136.10   $136.10  
  Purchase #3 $83.73   11.802%   $93.6118   $93.61   $93.60   $93.60  
  Purchase #4 $182.63   9.636%   $200.2282   $200.23   $200.25   $200.20  
  Purchase #5 $208.77   3.214%   $215.4799   $215.48   $215.50   $215.50  
  Purchase #6 $52.61   9.611%   $57.6663   $57.67   $57.65   $57.70  
  Purchase #7 $62.25   8.708%   $67.6707   $67.67   $67.65   $67.70  
  7 purchase totals = $961.76       $1,038.5964   $1,038.60   $1,038.60   $1,038.70