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 $61.36   4.241%   $63.9623   $63.96   $63.95   $64.00  
  Purchase #2 $101.76   5.522%   $107.3792   $107.38   $107.40   $107.40  
  Purchase #3 $166.99   4.576%   $174.6315   $174.63   $174.65   $174.60  
  Purchase #4 $31.44   8.836%   $34.218   $34.22   $34.20   $34.20  
  Purchase #5 $24.64   9.692%   $27.0281   $27.03   $27.05   $27.00  
  Purchase #6 $122.27   4.671%   $127.9812   $127.98   $128.00   $128.00  
  Purchase #7 $250.58   10.800%   $277.6426   $277.64   $277.65   $277.60  
  7 purchase totals = $759.04       $812.8429   $812.84   $812.90   $812.80