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 $216.48   10.665%   $239.5676   $239.57   $239.55   $239.60  
  Purchase #2 $244.41   7.141%   $261.8633   $261.86   $261.85   $261.90  
  Purchase #3 $125.39   11.263%   $139.5127   $139.51   $139.50   $139.50  
  Purchase #4 $237.77   13.134%   $268.9987   $269.00   $269.00   $269.00  
  Purchase #5 $54.74   12.842%   $61.7697   $61.77   $61.75   $61.80  
  Purchase #6 $212.46   8.255%   $229.9986   $230.00   $230.00   $230.00  
  Purchase #7 $28.54   3.619%   $29.5729   $29.57   $29.55   $29.60  
  7 purchase totals = $1,119.79       $1,231.2835   $1,231.28   $1,231.20   $1,231.40