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 $222.79   8.236%   $241.139   $241.14   $241.15   $241.10  
  Purchase #2 $68.57   10.746%   $75.9385   $75.94   $75.95   $75.90  
  Purchase #3 $74.48   7.365%   $79.9655   $79.97   $79.95   $80.00  
  Purchase #4 $133.26   9.605%   $146.0596   $146.06   $146.05   $146.10  
  Purchase #5 $56.72   12.337%   $63.7175   $63.72   $63.70   $63.70  
  Purchase #6 $76.77   13.669%   $87.2637   $87.26   $87.25   $87.30  
  Purchase #7 $229.76   5.788%   $243.0585   $243.06   $243.05   $243.10  
  7 purchase totals = $862.35       $937.1423   $937.15   $937.10   $937.20