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 $240.58   11.826%   $269.031   $269.03   $269.05   $269.00  
  Purchase #2 $186.46   11.552%   $207.9999   $208.00   $208.00   $208.00  
  Purchase #3 $200.45   12.782%   $226.0715   $226.07   $226.05   $226.10  
  Purchase #4 $120.90   3.798%   $125.4918   $125.49   $125.50   $125.50  
  Purchase #5 $227.32   12.488%   $255.7077   $255.71   $255.70   $255.70  
  Purchase #6 $111.87   11.842%   $125.1176   $125.12   $125.10   $125.10  
  Purchase #7 $179.93   6.577%   $191.764   $191.76   $191.75   $191.80  
  7 purchase totals = $1,267.51       $1,401.1835   $1,401.18   $1,401.15   $1,401.20