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 $74.25   10.778%   $82.2527   $82.25   $82.25   $82.30  
  Purchase #2 $217.69   10.753%   $241.0982   $241.10   $241.10   $241.10  
  Purchase #3 $179.28   10.780%   $198.6064   $198.61   $198.60   $198.60  
  Purchase #4 $162.67   10.795%   $180.2302   $180.23   $180.25   $180.20  
  Purchase #5 $111.99   8.138%   $121.1037   $121.10   $121.10   $121.10  
  Purchase #6 $240.72   3.854%   $249.9973   $250.00   $250.00   $250.00  
  Purchase #7 $17.42   13.232%   $19.725   $19.73   $19.75   $19.70  
  7 purchase totals = $1,004.02       $1,093.0135   $1,093.02   $1,093.05   $1,093.00