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 $24.94   3.669%   $25.855   $25.86   $25.85   $25.90  
  Purchase #2 $173.80   9.573%   $190.4379   $190.44   $190.45   $190.40  
  Purchase #3 $234.81   13.553%   $266.6338   $266.63   $266.65   $266.60  
  Purchase #4 $242.55   11.337%   $270.0479   $270.05   $270.05   $270.00  
  Purchase #5 $245.73   4.614%   $257.068   $257.07   $257.05   $257.10  
  Purchase #6 $65.31   10.194%   $71.9677   $71.97   $71.95   $72.00  
  Purchase #7 $139.91   3.252%   $144.4599   $144.46   $144.45   $144.50  
  7 purchase totals = $1,127.05       $1,226.4702   $1,226.48   $1,226.45   $1,226.50