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 $66.27   4.851%   $69.4848   $69.48   $69.50   $69.50  
  Purchase #2 $246.45   13.737%   $280.3048   $280.30   $280.30   $280.30  
  Purchase #3 $239.76   9.305%   $262.0697   $262.07   $262.05   $262.10  
  Purchase #4 $218.89   4.761%   $229.3114   $229.31   $229.30   $229.30  
  Purchase #5 $196.52   8.593%   $213.407   $213.41   $213.40   $213.40  
  Purchase #6 $183.48   3.605%   $190.0945   $190.09   $190.10   $190.10  
  Purchase #7 $11.60   6.475%   $12.3511   $12.35   $12.35   $12.40  
  7 purchase totals = $1,162.97       $1,257.0233   $1,257.01   $1,257.00   $1,257.10