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 $207.25   6.566%   $220.858   $220.86   $220.85   $220.90  
  Purchase #2 $125.77   4.117%   $130.948   $130.95   $130.95   $130.90  
  Purchase #3 $156.95   8.757%   $170.6941   $170.69   $170.70   $170.70  
  Purchase #4 $155.94   5.464%   $164.4606   $164.46   $164.45   $164.50  
  Purchase #5 $21.30   13.202%   $24.112   $24.11   $24.10   $24.10  
  Purchase #6 $147.59   7.532%   $158.7065   $158.71   $158.70   $158.70  
  Purchase #7 $125.77   11.851%   $140.675   $140.68   $140.70   $140.70  
  7 purchase totals = $940.57       $1,010.4542   $1,010.46   $1,010.45   $1,010.50