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 $239.54   8.748%   $260.495   $260.50   $260.50   $260.50  
  Purchase #2 $65.59   6.645%   $69.9485   $69.95   $69.95   $69.90  
  Purchase #3 $52.60   11.442%   $58.6185   $58.62   $58.60   $58.60  
  Purchase #4 $137.36   11.202%   $152.7471   $152.75   $152.75   $152.70  
  Purchase #5 $195.91   6.554%   $208.7499   $208.75   $208.75   $208.70  
  Purchase #6 $44.98   5.209%   $47.323   $47.32   $47.30   $47.30  
  Purchase #7 $6.58   13.512%   $7.4691   $7.47   $7.45   $7.50  
  7 purchase totals = $742.56       $805.3511   $805.36   $805.30   $805.20