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 $60.53   8.397%   $65.6127   $65.61   $65.60   $65.60  
  Purchase #2 $109.62   4.651%   $114.7184   $114.72   $114.70   $114.70  
  Purchase #3 $190.93   11.143%   $212.2053   $212.21   $212.20   $212.20  
  Purchase #4 $59.52   4.149%   $61.9895   $61.99   $62.00   $62.00  
  Purchase #5 $239.32   4.797%   $250.8002   $250.80   $250.80   $250.80  
  Purchase #6 $72.46   3.706%   $75.1454   $75.15   $75.15   $75.10  
  Purchase #7 $78.40   7.524%   $84.2988   $84.30   $84.30   $84.30  
  7 purchase totals = $810.78       $864.7703   $864.78   $864.75   $864.70