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 $220.50   9.193%   $240.7706   $240.77   $240.75   $240.80  
  Purchase #2 $161.25   6.715%   $172.0779   $172.08   $172.10   $172.10  
  Purchase #3 $38.89   11.688%   $43.4355   $43.44   $43.45   $43.40  
  Purchase #4 $9.58   7.706%   $10.3182   $10.32   $10.30   $10.30  
  Purchase #5 $219.62   13.703%   $249.7145   $249.71   $249.70   $249.70  
  Purchase #6 $127.62   9.827%   $140.1612   $140.16   $140.15   $140.20  
  Purchase #7 $142.99   4.360%   $149.2244   $149.22   $149.20   $149.20  
  7 purchase totals = $920.45       $1,005.7023   $1,005.70   $1,005.65   $1,005.70