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 $95.81   8.365%   $103.8245   $103.82   $103.80   $103.80  
  Purchase #2 $30.26   8.652%   $32.8781   $32.88   $32.90   $32.90  
  Purchase #3 $174.85   6.151%   $185.605   $185.61   $185.60   $185.60  
  Purchase #4 $151.91   6.407%   $161.6429   $161.64   $161.65   $161.60  
  Purchase #5 $127.60   8.528%   $138.4817   $138.48   $138.50   $138.50  
  Purchase #6 $158.57   11.826%   $177.3225   $177.32   $177.30   $177.30  
  Purchase #7 $224.57   12.592%   $252.8479   $252.85   $252.85   $252.80  
  7 purchase totals = $963.57       $1,052.6026   $1,052.60   $1,052.60   $1,052.50