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 $234.83   11.362%   $261.5114   $261.51   $261.50   $261.50  
  Purchase #2 $175.34   7.407%   $188.3274   $188.33   $188.35   $188.30  
  Purchase #3 $241.62   8.291%   $261.6527   $261.65   $261.65   $261.70  
  Purchase #4 $240.33   13.833%   $273.5748   $273.57   $273.55   $273.60  
  Purchase #5 $233.74   13.769%   $265.9237   $265.92   $265.90   $265.90  
  Purchase #6 $60.53   11.135%   $67.27   $67.27   $67.25   $67.30  
  Purchase #7 $106.96   11.159%   $118.8957   $118.90   $118.90   $118.90  
  7 purchase totals = $1,293.35       $1,437.1557   $1,437.15   $1,437.10   $1,437.20