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 $49.34   13.254%   $55.8795   $55.88   $55.90   $55.90  
  Purchase #2 $226.88   3.226%   $234.1991   $234.20   $234.20   $234.20  
  Purchase #3 $19.42   13.622%   $22.0654   $22.07   $22.05   $22.10  
  Purchase #4 $187.70   8.744%   $204.1125   $204.11   $204.10   $204.10  
  Purchase #5 $124.83   13.440%   $141.6072   $141.61   $141.60   $141.60  
  Purchase #6 $167.41   5.462%   $176.5539   $176.55   $176.55   $176.60  
  Purchase #7 $106.43   11.125%   $118.2703   $118.27   $118.25   $118.30  
  7 purchase totals = $882.01       $952.6879   $952.69   $952.65   $952.80