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 $189.83   12.701%   $213.9403   $213.94   $213.95   $213.90  
  Purchase #2 $172.77   12.265%   $193.9602   $193.96   $193.95   $194.00  
  Purchase #3 $149.32   9.696%   $163.7981   $163.80   $163.80   $163.80  
  Purchase #4 $28.91   11.401%   $32.206   $32.21   $32.20   $32.20  
  Purchase #5 $231.47   10.713%   $256.2674   $256.27   $256.25   $256.30  
  Purchase #6 $192.54   11.193%   $214.091   $214.09   $214.10   $214.10  
  Purchase #7 $240.53   8.714%   $261.4898   $261.49   $261.50   $261.50  
  7 purchase totals = $1,205.37       $1,335.7528   $1,335.76   $1,335.75   $1,335.80