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 $241.55   8.858%   $262.9465   $262.95   $262.95   $262.90  
  Purchase #2 $191.28   3.426%   $197.8333   $197.83   $197.85   $197.80  
  Purchase #3 $58.38   11.492%   $65.089   $65.09   $65.10   $65.10  
  Purchase #4 $71.86   6.507%   $76.5359   $76.54   $76.55   $76.50  
  Purchase #5 $214.52   3.669%   $222.3907   $222.39   $222.40   $222.40  
  Purchase #6 $105.66   4.797%   $110.7285   $110.73   $110.75   $110.70  
  Purchase #7 $58.58   3.874%   $60.8494   $60.85   $60.85   $60.80  
  7 purchase totals = $941.83       $996.3733   $996.38   $996.45   $996.20