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 $224.54   6.638%   $239.445   $239.45   $239.45   $239.40  
  Purchase #2 $55.64   9.846%   $61.1183   $61.12   $61.10   $61.10  
  Purchase #3 $69.69   9.324%   $76.1879   $76.19   $76.20   $76.20  
  Purchase #4 $174.75   4.809%   $183.1537   $183.15   $183.15   $183.20  
  Purchase #5 $247.77   9.759%   $271.9499   $271.95   $271.95   $271.90  
  Purchase #6 $22.76   7.561%   $24.4809   $24.48   $24.50   $24.50  
  Purchase #7 $242.67   7.738%   $261.4478   $261.45   $261.45   $261.40  
  7 purchase totals = $1,037.82       $1,117.7835   $1,117.79   $1,117.80   $1,117.70