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 $40.36   3.851%   $41.9143   $41.91   $41.90   $41.90  
  Purchase #2 $54.94   5.651%   $58.0447   $58.04   $58.05   $58.00  
  Purchase #3 $93.50   10.791%   $103.5896   $103.59   $103.60   $103.60  
  Purchase #4 $208.63   8.359%   $226.0694   $226.07   $226.05   $226.10  
  Purchase #5 $212.66   9.119%   $232.0525   $232.05   $232.05   $232.10  
  Purchase #6 $92.79   11.128%   $103.1157   $103.12   $103.10   $103.10  
  Purchase #7 $184.99   5.338%   $194.8648   $194.86   $194.85   $194.90  
  7 purchase totals = $887.87       $959.6510   $959.64   $959.60   $959.70