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 $199.46   8.804%   $217.0205   $217.02   $217.00   $217.00  
  Purchase #2 $49.34   11.524%   $55.0259   $55.03   $55.05   $55.00  
  Purchase #3 $138.60   6.357%   $147.4108   $147.41   $147.40   $147.40  
  Purchase #4 $77.73   4.799%   $81.4603   $81.46   $81.45   $81.50  
  Purchase #5 $35.99   12.236%   $40.3937   $40.39   $40.40   $40.40  
  Purchase #6 $210.27   6.826%   $224.623   $224.62   $224.60   $224.60  
  Purchase #7 $211.59   4.190%   $220.4556   $220.46   $220.45   $220.50  
  7 purchase totals = $922.98       $986.3898   $986.39   $986.35   $986.40