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 $61.72   10.414%   $68.1475   $68.15   $68.15   $68.10  
  Purchase #2 $32.57   9.477%   $35.6567   $35.66   $35.65   $35.70  
  Purchase #3 $21.94   7.366%   $23.5561   $23.56   $23.55   $23.60  
  Purchase #4 $208.93   11.264%   $232.4639   $232.46   $232.45   $232.50  
  Purchase #5 $106.81   9.425%   $116.8768   $116.88   $116.90   $116.90  
  Purchase #6 $218.43   10.818%   $242.0598   $242.06   $242.05   $242.10  
  Purchase #7 $68.58   3.431%   $70.933   $70.93   $70.95   $70.90  
  7 purchase totals = $718.98       $789.6938   $789.70   $789.70   $789.80