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 $125.79   8.723%   $136.7627   $136.76   $136.75   $136.80  
  Purchase #2 $125.75   10.302%   $138.7048   $138.70   $138.70   $138.70  
  Purchase #3 $44.78   9.754%   $49.1478   $49.15   $49.15   $49.10  
  Purchase #4 $239.29   11.544%   $266.9136   $266.91   $266.90   $266.90  
  Purchase #5 $231.70   3.179%   $239.0657   $239.07   $239.05   $239.10  
  Purchase #6 $124.36   11.662%   $138.8629   $138.86   $138.85   $138.90  
  Purchase #7 $227.33   5.681%   $240.2446   $240.24   $240.25   $240.20  
  7 purchase totals = $1,119.00       $1,209.7021   $1,209.69   $1,209.65   $1,209.70