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 $246.89   8.813%   $268.6484   $268.65   $268.65   $268.60  
  Purchase #2 $90.58   9.376%   $99.0728   $99.07   $99.05   $99.10  
  Purchase #3 $179.43   3.569%   $185.8339   $185.83   $185.85   $185.80  
  Purchase #4 $129.88   4.284%   $135.4441   $135.44   $135.45   $135.40  
  Purchase #5 $74.25   9.497%   $81.3015   $81.30   $81.30   $81.30  
  Purchase #6 $71.43   13.591%   $81.1381   $81.14   $81.15   $81.10  
  Purchase #7 $101.74   10.770%   $112.6974   $112.70   $112.70   $112.70  
  7 purchase totals = $894.20       $964.1362   $964.13   $964.15   $964.00