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 $232.41   10.698%   $257.2732   $257.27   $257.25   $257.30  
  Purchase #2 $243.45   6.785%   $259.9681   $259.97   $259.95   $260.00  
  Purchase #3 $91.57   5.225%   $96.3545   $96.35   $96.35   $96.40  
  Purchase #4 $73.78   3.298%   $76.2133   $76.21   $76.20   $76.20  
  Purchase #5 $105.88   9.158%   $115.5765   $115.58   $115.60   $115.60  
  Purchase #6 $85.26   6.292%   $90.6246   $90.62   $90.60   $90.60  
  Purchase #7 $233.50   8.583%   $253.5413   $253.54   $253.55   $253.50  
  7 purchase totals = $1,065.85       $1,149.5515   $1,149.54   $1,149.50   $1,149.60