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 $57.64   12.435%   $64.8075   $64.81   $64.80   $64.80  
  Purchase #2 $167.83   6.773%   $179.1971   $179.20   $179.20   $179.20  
  Purchase #3 $222.31   11.448%   $247.76   $247.76   $247.75   $247.80  
  Purchase #4 $191.95   6.493%   $204.4133   $204.41   $204.40   $204.40  
  Purchase #5 $215.46   5.589%   $227.5021   $227.50   $227.50   $227.50  
  Purchase #6 $183.73   12.394%   $206.5015   $206.50   $206.50   $206.50  
  Purchase #7 $66.68   13.836%   $75.9058   $75.91   $75.90   $75.90  
  7 purchase totals = $1,105.60       $1,206.0873   $1,206.09   $1,206.05   $1,206.10