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 $21.53   11.665%   $24.0415   $24.04   $24.05   $24.00  
  Purchase #2 $244.87   12.303%   $274.9964   $275.00   $275.00   $275.00  
  Purchase #3 $38.99   8.109%   $42.1517   $42.15   $42.15   $42.20  
  Purchase #4 $95.38   11.774%   $106.61   $106.61   $106.60   $106.60  
  Purchase #5 $26.57   11.647%   $29.6646   $29.66   $29.65   $29.70  
  Purchase #6 $164.86   5.863%   $174.5257   $174.53   $174.55   $174.50  
  Purchase #7 $51.63   4.125%   $53.7597   $53.76   $53.75   $53.80  
  7 purchase totals = $643.83       $705.7496   $705.75   $705.75   $705.80