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 $224.65   11.269%   $249.9658   $249.97   $249.95   $250.00  
  Purchase #2 $175.25   10.467%   $193.5934   $193.59   $193.60   $193.60  
  Purchase #3 $220.51   11.284%   $245.3923   $245.39   $245.40   $245.40  
  Purchase #4 $247.38   4.283%   $257.9753   $257.98   $258.00   $258.00  
  Purchase #5 $140.66   9.126%   $153.4966   $153.50   $153.50   $153.50  
  Purchase #6 $134.41   7.699%   $144.7582   $144.76   $144.75   $144.80  
  Purchase #7 $207.51   5.720%   $219.3796   $219.38   $219.40   $219.40  
  7 purchase totals = $1,350.37       $1,464.5612   $1,464.57   $1,464.60   $1,464.70