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 $146.48   12.727%   $165.1225   $165.12   $165.10   $165.10  
  Purchase #2 $240.64   10.302%   $265.4307   $265.43   $265.45   $265.40  
  Purchase #3 $113.69   7.706%   $122.451   $122.45   $122.45   $122.50  
  Purchase #4 $68.97   3.200%   $71.177   $71.18   $71.20   $71.20  
  Purchase #5 $242.32   5.587%   $255.8584   $255.86   $255.85   $255.90  
  Purchase #6 $151.63   8.134%   $163.9636   $163.96   $163.95   $164.00  
  Purchase #7 $114.27   3.613%   $118.3986   $118.40   $118.40   $118.40  
  7 purchase totals = $1,078.00       $1,162.4018   $1,162.40   $1,162.40   $1,162.50