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 $103.86   12.271%   $116.6047   $116.60   $116.60   $116.60  
  Purchase #2 $110.64   4.791%   $115.9408   $115.94   $115.95   $115.90  
  Purchase #3 $174.95   10.299%   $192.9681   $192.97   $192.95   $193.00  
  Purchase #4 $122.52   10.397%   $135.2584   $135.26   $135.25   $135.30  
  Purchase #5 $111.87   13.177%   $126.6111   $126.61   $126.60   $126.60  
  Purchase #6 $155.65   4.478%   $162.62   $162.62   $162.60   $162.60  
  Purchase #7 $72.40   12.796%   $81.6643   $81.66   $81.65   $81.70  
  7 purchase totals = $851.89       $931.6674   $931.66   $931.60   $931.70