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 $55.45   11.129%   $61.621   $61.62   $61.60   $61.60  
  Purchase #2 $48.86   7.188%   $52.3721   $52.37   $52.35   $52.40  
  Purchase #3 $67.73   13.178%   $76.6555   $76.66   $76.65   $76.70  
  Purchase #4 $207.70   3.754%   $215.4971   $215.50   $215.50   $215.50  
  Purchase #5 $244.80   3.289%   $252.8515   $252.85   $252.85   $252.90  
  Purchase #6 $15.47   12.353%   $17.381   $17.38   $17.40   $17.40  
  Purchase #7 $64.80   4.268%   $67.5657   $67.57   $67.55   $67.60  
  7 purchase totals = $704.81       $743.9439   $743.95   $743.90   $744.10