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 $108.32   12.802%   $122.1871   $122.19   $122.20   $122.20  
  Purchase #2 $67.72   10.150%   $74.5936   $74.59   $74.60   $74.60  
  Purchase #3 $214.87   12.723%   $242.2079   $242.21   $242.20   $242.20  
  Purchase #4 $200.46   12.609%   $225.736   $225.74   $225.75   $225.70  
  Purchase #5 $242.83   3.617%   $251.6132   $251.61   $251.60   $251.60  
  Purchase #6 $192.81   8.164%   $208.551   $208.55   $208.55   $208.60  
  Purchase #7 $206.99   10.663%   $229.0613   $229.06   $229.05   $229.10  
  7 purchase totals = $1,234.00       $1,353.9501   $1,353.95   $1,353.95   $1,354.00