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 $66.97   5.448%   $70.6185   $70.62   $70.60   $70.60  
  Purchase #2 $175.43   13.117%   $198.4412   $198.44   $198.45   $198.40  
  Purchase #3 $215.97   13.105%   $244.2729   $244.27   $244.25   $244.30  
  Purchase #4 $162.48   8.128%   $175.6864   $175.69   $175.70   $175.70  
  Purchase #5 $227.74   6.139%   $241.721   $241.72   $241.70   $241.70  
  Purchase #6 $205.32   4.362%   $214.2761   $214.28   $214.30   $214.30  
  Purchase #7 $227.94   5.762%   $241.0739   $241.07   $241.05   $241.10  
  7 purchase totals = $1,281.85       $1,386.0900   $1,386.09   $1,386.05   $1,386.10