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 $92.83   6.585%   $98.9429   $98.94   $98.95   $98.90  
  Purchase #2 $44.83   11.595%   $50.028   $50.03   $50.05   $50.00  
  Purchase #3 $73.92   5.469%   $77.9627   $77.96   $77.95   $78.00  
  Purchase #4 $198.92   7.472%   $213.7833   $213.78   $213.80   $213.80  
  Purchase #5 $211.26   13.400%   $239.5688   $239.57   $239.55   $239.60  
  Purchase #6 $116.34   7.422%   $124.9748   $124.97   $124.95   $125.00  
  Purchase #7 $129.42   6.260%   $137.5217   $137.52   $137.50   $137.50  
  7 purchase totals = $867.52       $942.7822   $942.77   $942.75   $942.80