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 $225.57   11.788%   $252.1602   $252.16   $252.15   $252.20  
  Purchase #2 $163.33   13.832%   $185.9218   $185.92   $185.90   $185.90  
  Purchase #3 $248.36   5.443%   $261.8782   $261.88   $261.90   $261.90  
  Purchase #4 $205.96   9.573%   $225.6766   $225.68   $225.70   $225.70  
  Purchase #5 $182.46   10.539%   $201.6895   $201.69   $201.70   $201.70  
  Purchase #6 $227.80   11.721%   $254.5004   $254.50   $254.50   $254.50  
  Purchase #7 $142.78   6.524%   $152.095   $152.10   $152.10   $152.10  
  7 purchase totals = $1,396.26       $1,533.9217   $1,533.93   $1,533.95   $1,534.00