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 $232.85   10.181%   $256.5565   $256.56   $256.55   $256.60  
  Purchase #2 $241.69   7.121%   $258.9007   $258.90   $258.90   $258.90  
  Purchase #3 $119.70   5.104%   $125.8095   $125.81   $125.80   $125.80  
  Purchase #4 $26.43   13.760%   $30.0668   $30.07   $30.05   $30.10  
  Purchase #5 $176.69   9.597%   $193.6469   $193.65   $193.65   $193.60  
  Purchase #6 $208.95   12.565%   $235.2046   $235.20   $235.20   $235.20  
  Purchase #7 $214.89   12.812%   $242.4217   $242.42   $242.40   $242.40  
  7 purchase totals = $1,221.20       $1,342.6067   $1,342.61   $1,342.55   $1,342.60