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 $188.63   10.291%   $208.0419   $208.04   $208.05   $208.00  
  Purchase #2 $131.50   8.799%   $143.0707   $143.07   $143.05   $143.10  
  Purchase #3 $62.70   11.225%   $69.7381   $69.74   $69.75   $69.70  
  Purchase #4 $26.68   11.549%   $29.7613   $29.76   $29.75   $29.80  
  Purchase #5 $221.57   13.507%   $251.4975   $251.50   $251.50   $251.50  
  Purchase #6 $160.77   11.263%   $178.8775   $178.88   $178.90   $178.90  
  Purchase #7 $66.66   5.564%   $70.369   $70.37   $70.35   $70.40  
  7 purchase totals = $858.51       $951.3560   $951.36   $951.35   $951.40