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 $246.51   6.384%   $262.2472   $262.25   $262.25   $262.20  
  Purchase #2 $111.40   3.549%   $115.3536   $115.35   $115.35   $115.40  
  Purchase #3 $165.43   4.706%   $173.2151   $173.22   $173.20   $173.20  
  Purchase #4 $70.41   13.340%   $79.8027   $79.80   $79.80   $79.80  
  Purchase #5 $153.59   3.204%   $158.511   $158.51   $158.50   $158.50  
  Purchase #6 $248.73   4.283%   $259.3831   $259.38   $259.40   $259.40  
  Purchase #7 $228.30   3.354%   $235.9572   $235.96   $235.95   $236.00  
  7 purchase totals = $1,224.37       $1,284.4699   $1,284.47   $1,284.45   $1,284.50