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 $201.29   12.613%   $226.6787   $226.68   $226.70   $226.70  
  Purchase #2 $54.36   10.853%   $60.2597   $60.26   $60.25   $60.30  
  Purchase #3 $122.32   12.191%   $137.232   $137.23   $137.25   $137.20  
  Purchase #4 $236.41   11.634%   $263.9139   $263.91   $263.90   $263.90  
  Purchase #5 $163.55   7.474%   $175.7737   $175.77   $175.75   $175.80  
  Purchase #6 $70.75   5.278%   $74.4842   $74.48   $74.50   $74.50  
  Purchase #7 $51.91   6.292%   $55.1762   $55.18   $55.20   $55.20  
  7 purchase totals = $900.59       $993.5184   $993.51   $993.55   $993.60