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 $234.93   13.451%   $266.5304   $266.53   $266.55   $266.50  
  Purchase #2 $104.91   7.274%   $112.5412   $112.54   $112.55   $112.50  
  Purchase #3 $14.74   5.187%   $15.5046   $15.50   $15.50   $15.50  
  Purchase #4 $6.43   11.411%   $7.1637   $7.16   $7.15   $7.20  
  Purchase #5 $70.85   4.573%   $74.09   $74.09   $74.10   $74.10  
  Purchase #6 $110.73   5.279%   $116.5754   $116.58   $116.60   $116.60  
  Purchase #7 $119.81   9.835%   $131.5933   $131.59   $131.60   $131.60  
  7 purchase totals = $662.40       $723.9986   $723.99   $724.05   $724.00