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 $47.63   10.197%   $52.4868   $52.49   $52.50   $52.50  
  Purchase #2 $215.38   5.278%   $226.7478   $226.75   $226.75   $226.70  
  Purchase #3 $29.26   3.685%   $30.3382   $30.34   $30.35   $30.30  
  Purchase #4 $214.26   4.717%   $224.3666   $224.37   $224.35   $224.40  
  Purchase #5 $120.99   4.314%   $126.2095   $126.21   $126.20   $126.20  
  Purchase #6 $121.72   5.615%   $128.5546   $128.55   $128.55   $128.60  
  Purchase #7 $205.54   10.579%   $227.2841   $227.28   $227.30   $227.30  
  7 purchase totals = $954.78       $1,015.9876   $1,015.99   $1,016.00   $1,016.00