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 $45.41   9.477%   $49.7135   $49.71   $49.70   $49.70  
  Purchase #2 $28.91   12.164%   $32.4266   $32.43   $32.45   $32.40  
  Purchase #3 $242.76   12.486%   $273.071   $273.07   $273.05   $273.10  
  Purchase #4 $119.90   3.270%   $123.8207   $123.82   $123.80   $123.80  
  Purchase #5 $190.40   4.106%   $198.2178   $198.22   $198.20   $198.20  
  Purchase #6 $113.41   10.373%   $125.174   $125.17   $125.15   $125.20  
  Purchase #7 $243.30   7.788%   $262.2482   $262.25   $262.25   $262.20  
  7 purchase totals = $984.09       $1,064.6718   $1,064.67   $1,064.60   $1,064.60