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 $188.31   13.671%   $214.0539   $214.05   $214.05   $214.10  
  Purchase #2 $133.35   8.486%   $144.6661   $144.67   $144.65   $144.70  
  Purchase #3 $191.90   4.423%   $200.3877   $200.39   $200.40   $200.40  
  Purchase #4 $67.37   9.368%   $73.6812   $73.68   $73.70   $73.70  
  Purchase #5 $182.26   13.185%   $206.291   $206.29   $206.30   $206.30  
  Purchase #6 $26.65   3.676%   $27.6297   $27.63   $27.65   $27.60  
  Purchase #7 $126.32   10.433%   $139.499   $139.50   $139.50   $139.50  
  7 purchase totals = $916.16       $1,006.2086   $1,006.21   $1,006.25   $1,006.30