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 $241.99   11.421%   $269.6277   $269.63   $269.65   $269.60  
  Purchase #2 $111.58   9.406%   $122.0752   $122.08   $122.10   $122.10  
  Purchase #3 $32.89   5.200%   $34.6003   $34.60   $34.60   $34.60  
  Purchase #4 $191.74   6.783%   $204.7457   $204.75   $204.75   $204.70  
  Purchase #5 $200.69   7.850%   $216.4442   $216.44   $216.45   $216.40  
  Purchase #6 $86.59   10.115%   $95.3486   $95.35   $95.35   $95.30  
  Purchase #7 $52.76   7.399%   $56.6637   $56.66   $56.65   $56.70  
  7 purchase totals = $918.24       $999.5054   $999.51   $999.55   $999.40