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 $38.82   5.726%   $41.0428   $41.04   $41.05   $41.00  
  Purchase #2 $131.86   8.275%   $142.7714   $142.77   $142.75   $142.80  
  Purchase #3 $44.79   13.327%   $50.7592   $50.76   $50.75   $50.80  
  Purchase #4 $236.97   10.384%   $261.577   $261.58   $261.60   $261.60  
  Purchase #5 $236.77   10.426%   $261.4556   $261.46   $261.45   $261.50  
  Purchase #6 $172.65   8.744%   $187.7465   $187.75   $187.75   $187.70  
  Purchase #7 $68.75   9.137%   $75.0317   $75.03   $75.05   $75.00  
  7 purchase totals = $930.61       $1,020.3842   $1,020.39   $1,020.40   $1,020.40