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 $30.56   11.182%   $33.9772   $33.98   $34.00   $34.00  
  Purchase #2 $88.61   7.691%   $95.425   $95.43   $95.45   $95.40  
  Purchase #3 $232.63   10.438%   $256.9119   $256.91   $256.90   $256.90  
  Purchase #4 $168.66   6.490%   $179.606   $179.61   $179.60   $179.60  
  Purchase #5 $229.67   3.351%   $237.3662   $237.37   $237.35   $237.40  
  Purchase #6 $181.25   13.783%   $206.2317   $206.23   $206.25   $206.20  
  Purchase #7 $188.89   4.203%   $196.829   $196.83   $196.85   $196.80  
  7 purchase totals = $1,120.27       $1,206.3470   $1,206.36   $1,206.40   $1,206.30