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 $221.55   6.613%   $236.2011   $236.20   $236.20   $236.20  
  Purchase #2 $131.64   11.619%   $146.9353   $146.94   $146.95   $146.90  
  Purchase #3 $31.39   5.561%   $33.1356   $33.14   $33.15   $33.10  
  Purchase #4 $198.88   10.730%   $220.2198   $220.22   $220.20   $220.20  
  Purchase #5 $199.44   12.347%   $224.0649   $224.06   $224.05   $224.10  
  Purchase #6 $131.95   12.220%   $148.0743   $148.07   $148.05   $148.10  
  Purchase #7 $186.87   3.111%   $192.6835   $192.68   $192.70   $192.70  
  7 purchase totals = $1,101.72       $1,201.3145   $1,201.31   $1,201.30   $1,201.30