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 $61.85   5.104%   $65.0068   $65.01   $65.00   $65.00  
  Purchase #2 $122.76   6.713%   $131.0009   $131.00   $131.00   $131.00  
  Purchase #3 $197.47   12.539%   $222.2308   $222.23   $222.25   $222.20  
  Purchase #4 $15.66   3.849%   $16.2628   $16.26   $16.25   $16.30  
  Purchase #5 $89.81   3.441%   $92.9004   $92.90   $92.90   $92.90  
  Purchase #6 $162.39   9.374%   $177.6124   $177.61   $177.60   $177.60  
  Purchase #7 $50.49   5.397%   $53.2149   $53.21   $53.20   $53.20  
  7 purchase totals = $700.43       $758.2290   $758.22   $758.20   $758.20