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 $24.42   8.458%   $26.4854   $26.49   $26.50   $26.50  
  Purchase #2 $225.49   7.563%   $242.5438   $242.54   $242.55   $242.50  
  Purchase #3 $192.25   4.638%   $201.1666   $201.17   $201.15   $201.20  
  Purchase #4 $68.77   5.109%   $72.2835   $72.28   $72.30   $72.30  
  Purchase #5 $108.51   7.685%   $116.849   $116.85   $116.85   $116.80  
  Purchase #6 $227.45   7.695%   $244.9523   $244.95   $244.95   $245.00  
  Purchase #7 $104.39   6.749%   $111.4353   $111.44   $111.45   $111.40  
  7 purchase totals = $951.28       $1,015.7159   $1,015.72   $1,015.75   $1,015.70