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 $31.61   12.212%   $35.4702   $35.47   $35.45   $35.50  
  Purchase #2 $231.47   6.522%   $246.5665   $246.57   $246.55   $246.60  
  Purchase #3 $58.36   8.379%   $63.25   $63.25   $63.25   $63.30  
  Purchase #4 $43.36   4.294%   $45.2219   $45.22   $45.20   $45.20  
  Purchase #5 $77.67   9.493%   $85.0432   $85.04   $85.05   $85.00  
  Purchase #6 $214.56   4.538%   $224.2967   $224.30   $224.30   $224.30  
  Purchase #7 $6.86   12.493%   $7.717   $7.72   $7.70   $7.70  
  7 purchase totals = $663.89       $707.5655   $707.57   $707.50   $707.60