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 $237.77   11.451%   $264.997   $265.00   $265.00   $265.00  
  Purchase #2 $129.59   5.484%   $136.6967   $136.70   $136.70   $136.70  
  Purchase #3 $41.62   3.277%   $42.9839   $42.98   $43.00   $43.00  
  Purchase #4 $71.58   7.522%   $76.9642   $76.96   $76.95   $77.00  
  Purchase #5 $173.45   6.361%   $184.4832   $184.48   $184.50   $184.50  
  Purchase #6 $180.72   3.158%   $186.4271   $186.43   $186.45   $186.40  
  Purchase #7 $6.83   12.618%   $7.6918   $7.69   $7.70   $7.70  
  7 purchase totals = $841.56       $900.2439   $900.24   $900.30   $900.30