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 $242.88   9.207%   $265.242   $265.24   $265.25   $265.20  
  Purchase #2 $45.39   3.131%   $46.8112   $46.81   $46.80   $46.80  
  Purchase #3 $166.78   13.773%   $189.7506   $189.75   $189.75   $189.80  
  Purchase #4 $81.68   6.349%   $86.8659   $86.87   $86.85   $86.90  
  Purchase #5 $73.39   5.115%   $77.1439   $77.14   $77.15   $77.10  
  Purchase #6 $206.46   5.343%   $217.4912   $217.49   $217.50   $217.50  
  Purchase #7 $56.69   5.419%   $59.762   $59.76   $59.75   $59.80  
  7 purchase totals = $873.27       $943.0668   $943.06   $943.05   $943.10