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 $22.40   7.224%   $24.0182   $24.02   $24.00   $24.00  
  Purchase #2 $58.69   11.174%   $65.248   $65.25   $65.25   $65.20  
  Purchase #3 $63.88   10.212%   $70.4034   $70.40   $70.40   $70.40  
  Purchase #4 $51.73   13.206%   $58.5615   $58.56   $58.55   $58.60  
  Purchase #5 $54.26   7.724%   $58.451   $58.45   $58.45   $58.50  
  Purchase #6 $144.50   4.701%   $151.2929   $151.29   $151.30   $151.30  
  Purchase #7 $69.61   11.288%   $77.4676   $77.47   $77.45   $77.50  
  7 purchase totals = $465.07       $505.4426   $505.44   $505.40   $505.50