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 $55.67   9.696%   $61.0678   $61.07   $61.05   $61.10  
  Purchase #2 $168.33   4.280%   $175.5345   $175.53   $175.55   $175.50  
  Purchase #3 $20.33   4.259%   $21.1959   $21.20   $21.20   $21.20  
  Purchase #4 $83.83   11.336%   $93.333   $93.33   $93.35   $93.30  
  Purchase #5 $173.71   5.328%   $182.9653   $182.97   $182.95   $183.00  
  Purchase #6 $103.75   12.422%   $116.6378   $116.64   $116.65   $116.60  
  Purchase #7 $121.38   5.343%   $127.8653   $127.87   $127.85   $127.90  
  7 purchase totals = $727.00       $778.5996   $778.61   $778.60   $778.60