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 $37.48   10.622%   $41.4611   $41.46   $41.45   $41.50  
  Purchase #2 $30.93   7.159%   $33.1443   $33.14   $33.15   $33.10  
  Purchase #3 $50.40   7.530%   $54.1951   $54.20   $54.20   $54.20  
  Purchase #4 $222.54   8.844%   $242.2214   $242.22   $242.20   $242.20  
  Purchase #5 $233.66   11.802%   $261.2366   $261.24   $261.25   $261.20  
  Purchase #6 $219.45   8.258%   $237.5722   $237.57   $237.55   $237.60  
  Purchase #7 $93.37   3.605%   $96.736   $96.74   $96.75   $96.70  
  7 purchase totals = $887.83       $966.5667   $966.57   $966.55   $966.50