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 $24.61   5.856%   $26.0512   $26.05   $26.05   $26.10  
  Purchase #2 $56.67   12.715%   $63.8756   $63.88   $63.90   $63.90  
  Purchase #3 $231.33   3.543%   $239.526   $239.53   $239.55   $239.50  
  Purchase #4 $157.54   6.534%   $167.8337   $167.83   $167.85   $167.80  
  Purchase #5 $225.95   6.627%   $240.9237   $240.92   $240.90   $240.90  
  Purchase #6 $233.80   13.536%   $265.4472   $265.45   $265.45   $265.40  
  Purchase #7 $28.31   5.394%   $29.837   $29.84   $29.85   $29.80  
  7 purchase totals = $958.21       $1,033.4944   $1,033.50   $1,033.55   $1,033.40