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 $29.86   12.851%   $33.6973   $33.70   $33.70   $33.70  
  Purchase #2 $229.55   9.818%   $252.0872   $252.09   $252.10   $252.10  
  Purchase #3 $114.86   7.546%   $123.5273   $123.53   $123.55   $123.50  
  Purchase #4 $189.82   11.518%   $211.6835   $211.68   $211.70   $211.70  
  Purchase #5 $229.25   5.623%   $242.1407   $242.14   $242.15   $242.10  
  Purchase #6 $106.61   12.725%   $120.1761   $120.18   $120.20   $120.20  
  Purchase #7 $26.71   5.683%   $28.2279   $28.23   $28.25   $28.20  
  7 purchase totals = $926.66       $1,011.5400   $1,011.55   $1,011.65   $1,011.50