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 $233.66   10.856%   $259.0261   $259.03   $259.05   $259.00  
  Purchase #2 $93.45   3.670%   $96.8796   $96.88   $96.90   $96.90  
  Purchase #3 $231.45   13.627%   $262.9897   $262.99   $263.00   $263.00  
  Purchase #4 $249.46   5.327%   $262.7487   $262.75   $262.75   $262.70  
  Purchase #5 $56.78   5.646%   $59.9858   $59.99   $60.00   $60.00  
  Purchase #6 $91.72   5.218%   $96.5059   $96.51   $96.50   $96.50  
  Purchase #7 $223.31   6.379%   $237.5549   $237.55   $237.55   $237.60  
  7 purchase totals = $1,179.83       $1,275.6907   $1,275.70   $1,275.75   $1,275.70