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 $22.82   8.771%   $24.8215   $24.82   $24.80   $24.80  
  Purchase #2 $30.90   10.746%   $34.2205   $34.22   $34.20   $34.20  
  Purchase #3 $218.38   8.368%   $236.654   $236.65   $236.65   $236.70  
  Purchase #4 $63.81   10.255%   $70.3537   $70.35   $70.35   $70.40  
  Purchase #5 $50.47   8.656%   $54.8387   $54.84   $54.85   $54.80  
  Purchase #6 $8.59   8.697%   $9.3371   $9.34   $9.35   $9.30  
  Purchase #7 $69.83   6.264%   $74.2042   $74.20   $74.20   $74.20  
  7 purchase totals = $464.80       $504.4297   $504.42   $504.40   $504.40