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 $229.95   5.644%   $242.9284   $242.93   $242.95   $242.90  
  Purchase #2 $22.59   3.391%   $23.356   $23.36   $23.35   $23.40  
  Purchase #3 $116.53   9.296%   $127.3626   $127.36   $127.35   $127.40  
  Purchase #4 $104.78   12.291%   $117.6585   $117.66   $117.65   $117.70  
  Purchase #5 $27.26   8.629%   $29.6123   $29.61   $29.60   $29.60  
  Purchase #6 $195.92   6.315%   $208.2923   $208.29   $208.30   $208.30  
  Purchase #7 $235.60   11.388%   $262.4301   $262.43   $262.45   $262.40  
  7 purchase totals = $932.63       $1,011.6402   $1,011.64   $1,011.65   $1,011.70