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 $50.46   6.673%   $53.8272   $53.83   $53.85   $53.80  
  Purchase #2 $151.81   11.720%   $169.6021   $169.60   $169.60   $169.60  
  Purchase #3 $116.83   5.862%   $123.6786   $123.68   $123.70   $123.70  
  Purchase #4 $202.48   7.547%   $217.7612   $217.76   $217.75   $217.80  
  Purchase #5 $22.95   6.860%   $24.5244   $24.52   $24.50   $24.50  
  Purchase #6 $152.31   11.138%   $169.2743   $169.27   $169.25   $169.30  
  Purchase #7 $190.75   5.509%   $201.2584   $201.26   $201.25   $201.30  
  7 purchase totals = $887.59       $959.9262   $959.92   $959.90   $960.00