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 $233.70   11.660%   $260.9494   $260.95   $260.95   $260.90  
  Purchase #2 $152.98   13.621%   $173.8174   $173.82   $173.80   $173.80  
  Purchase #3 $176.28   4.789%   $184.722   $184.72   $184.70   $184.70  
  Purchase #4 $201.91   11.334%   $224.7945   $224.79   $224.80   $224.80  
  Purchase #5 $228.45   6.165%   $242.5339   $242.53   $242.55   $242.50  
  Purchase #6 $127.62   7.382%   $137.0409   $137.04   $137.05   $137.00  
  Purchase #7 $41.76   5.702%   $44.1412   $44.14   $44.15   $44.10  
  7 purchase totals = $1,162.70       $1,267.9993   $1,267.99   $1,268.00   $1,267.80