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 $57.83   8.223%   $62.5854   $62.59   $62.60   $62.60  
  Purchase #2 $232.74   12.427%   $261.6626   $261.66   $261.65   $261.70  
  Purchase #3 $159.74   9.401%   $174.7572   $174.76   $174.75   $174.80  
  Purchase #4 $44.93   5.622%   $47.456   $47.46   $47.45   $47.50  
  Purchase #5 $175.57   4.464%   $183.4074   $183.41   $183.40   $183.40  
  Purchase #6 $230.65   4.698%   $241.4859   $241.49   $241.50   $241.50  
  Purchase #7 $31.55   7.316%   $33.8582   $33.86   $33.85   $33.90  
  7 purchase totals = $933.01       $1,005.2127   $1,005.23   $1,005.20   $1,005.40