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 $204.34   7.755%   $220.1866   $220.19   $220.20   $220.20  
  Purchase #2 $134.69   6.612%   $143.5957   $143.60   $143.60   $143.60  
  Purchase #3 $32.62   5.470%   $34.4043   $34.40   $34.40   $34.40  
  Purchase #4 $148.99   11.694%   $166.4129   $166.41   $166.40   $166.40  
  Purchase #5 $180.82   13.733%   $205.652   $205.65   $205.65   $205.70  
  Purchase #6 $38.55   5.757%   $40.7693   $40.77   $40.75   $40.80  
  Purchase #7 $43.76   4.262%   $45.6251   $45.63   $45.65   $45.60  
  7 purchase totals = $783.77       $856.6459   $856.65   $856.65   $856.70