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 $185.83   9.610%   $203.6883   $203.69   $203.70   $203.70  
  Purchase #2 $124.61   4.552%   $130.2822   $130.28   $130.30   $130.30  
  Purchase #3 $70.62   12.193%   $79.2307   $79.23   $79.25   $79.20  
  Purchase #4 $53.64   3.139%   $55.3238   $55.32   $55.30   $55.30  
  Purchase #5 $60.38   13.234%   $68.3707   $68.37   $68.35   $68.40  
  Purchase #6 $101.68   6.491%   $108.28   $108.28   $108.30   $108.30  
  Purchase #7 $171.60   8.788%   $186.6802   $186.68   $186.70   $186.70  
  7 purchase totals = $768.36       $831.8559   $831.85   $831.90   $831.90