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 $210.53   7.758%   $226.8629   $226.86   $226.85   $226.90  
  Purchase #2 $66.61   4.197%   $69.4056   $69.41   $69.40   $69.40  
  Purchase #3 $180.42   3.176%   $186.1501   $186.15   $186.15   $186.20  
  Purchase #4 $170.36   12.287%   $191.2921   $191.29   $191.30   $191.30  
  Purchase #5 $114.31   7.725%   $123.1404   $123.14   $123.15   $123.10  
  Purchase #6 $234.60   8.675%   $254.9516   $254.95   $254.95   $255.00  
  Purchase #7 $141.80   8.462%   $153.7991   $153.80   $153.80   $153.80  
  7 purchase totals = $1,118.63       $1,205.6018   $1,205.60   $1,205.60   $1,205.70