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 $24.93   8.457%   $27.0383   $27.04   $27.05   $27.00  
  Purchase #2 $42.39   7.481%   $45.5612   $45.56   $45.55   $45.60  
  Purchase #3 $247.84   13.247%   $280.6714   $280.67   $280.65   $280.70  
  Purchase #4 $11.61   4.162%   $12.0932   $12.09   $12.10   $12.10  
  Purchase #5 $107.57   7.748%   $115.9045   $115.90   $115.90   $115.90  
  Purchase #6 $239.47   7.347%   $257.0639   $257.06   $257.05   $257.10  
  Purchase #7 $18.97   5.240%   $19.964   $19.96   $19.95   $20.00  
  7 purchase totals = $692.78       $758.2965   $758.28   $758.25   $758.40