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 $126.71   10.699%   $140.2667   $140.27   $140.25   $140.30  
  Purchase #2 $154.91   7.759%   $166.9295   $166.93   $166.95   $166.90  
  Purchase #3 $139.63   7.608%   $150.2531   $150.25   $150.25   $150.30  
  Purchase #4 $208.55   13.481%   $236.6646   $236.66   $236.65   $236.70  
  Purchase #5 $237.43   5.279%   $249.9639   $249.96   $249.95   $250.00  
  Purchase #6 $88.77   10.682%   $98.2524   $98.25   $98.25   $98.30  
  Purchase #7 $148.60   6.296%   $157.9559   $157.96   $157.95   $158.00  
  7 purchase totals = $1,104.60       $1,200.2861   $1,200.28   $1,200.25   $1,200.50