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 $215.34   12.320%   $241.8699   $241.87   $241.85   $241.90  
  Purchase #2 $125.36   7.620%   $134.9124   $134.91   $134.90   $134.90  
  Purchase #3 $200.94   8.417%   $217.8531   $217.85   $217.85   $217.90  
  Purchase #4 $98.49   13.537%   $111.8226   $111.82   $111.80   $111.80  
  Purchase #5 $233.29   13.371%   $264.4832   $264.48   $264.50   $264.50  
  Purchase #6 $113.45   3.682%   $117.6272   $117.63   $117.65   $117.60  
  Purchase #7 $224.26   10.447%   $247.6884   $247.69   $247.70   $247.70  
  7 purchase totals = $1,211.13       $1,336.2568   $1,336.25   $1,336.25   $1,336.30